Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Significance was accepted for p values <0.05. Data is obtained during follicular phase.

Generalized estimating equation (GEE) with log link function and exchangeable correlation structure.

Significance was accepted for p values <0.05. Data is obtained during luteal phase.

Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Significance was accepted for p values <0.05. Data is obtained during follicular phase.

Generalized estimating equation (GEE) with log link function and exchangeable correlation structure.

Significance was accepted for p values <0.05. Data is obtained during luteal phase.

Females ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) or on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold, and pregnancy.

Additional exclusion criteria for female participants: History of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training, or currently participating in competitive level sports.

Males: Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, and medications that lower seizure threshold.

Significance was accepted for p values <0.05.

Repeated measures ANOVA

Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Significance was accepted for p values <0.05. Data obtained during active pill phase.

Generalized estimating equation (GEE) with log link function and exchangeable correlation structure.

Significance was accepted for p values <0.05. Data obtained during inactive pill phase.

Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Significance was accepted for p values <0.05. Data is obtained during follicular phase.

Generalized estimating equation (GEE) with log link function and exchangeable correlation structure.

Significance was accepted for p values <0.05. Data is obtained during luteal phase.

Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training, or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Significance was accepted for p values <0.05. Data is obtained during follicular phase.

Generalized estimating equation (GEE) with log link function and exchangeable correlation structure.

Significance was accepted for p values <0.05. Data is obtained during luteal phase.

Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training, or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Significance was accepted for p values <0.05. Data is obtained during follicular phase.

Generalized estimating equation (GEE) with log link function and exchangeable correlation structure.

Significance was accepted for p values <0.05. Data is obtained during luteal phase.

Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training, or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Significance was accepted for p values <0.05. Data is obtained during follicular phase.

Generalized estimating equation (GEE) with log link function and exchangeable correlation structure.

Significance was accepted for p values <0.05. Data is obtained during luteal phase.

Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training, or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Significance was accepted for p values <0.05. Data is obtained during active pill phase.

Generalized estimating equation (GEE) with log link function and exchangeable correlation structure.

Significance was accepted for p values <0.05. Data is obtained during inactive pill phase.

Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training, or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Significance was accepted for p values <0.05. Data is obtained during active pill phase.

Generalized estimating equation (GEE) with log link function and exchangeable correlation structure.

Significance was accepted for p values <0.05. Data is obtained during inactive pill phase.

Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training, or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Significance was accepted for p values <0.05. Data is obtained during active pill phase.

Generalized estimating equation (GEE) with log link function and exchangeable correlation structure.

Significance was accepted for p values <0.05. Data is obtained during inactive pill phase.

Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Significance was accepted for p values <0.05. Data is obtained from follicular phase.

Generalized estimating equation (GEE) with log link function and exchangeable correlation structure.

Significance was accepted for p values <0.05. Data is obtained from luteal phase.

Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training, or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Significance was accepted for p values <0.05. Data is obtained from follicular phase.

Generalized estimating equation (GEE) with log link function and exchangeable correlation structure.

Significance was accepted for p values <0.05. Data is obtained from luteal phase.

Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Significance was accepted for p values <0.05. Data is obtained from follicular phase.

Generalized estimating equation (GEE) with log link function and exchangeable correlation structure.

Significance was accepted for p values <0.05. Data is obtained from luteal phase.

Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Significance was accepted for p values <0.05. Data is obtained during active pill phase.

Generalized estimating equation (GEE) with log link function and exchangeable correlation structure.

Significance was accepted for p values <0.05. Data is obtained during inactive pill phase.

Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Significance was accepted for p values <0.05. Data is obtained during active pill phase.

Generalized estimating equation (GEE) with log link function and exchangeable correlation structure.

Significance was accepted for p values <0.05. Data is obtained during inactive pill phase.

Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Significance was accepted for p values <0.05. Data is obtained during active pill phase.

Generalized estimating equation (GEE) with log link function and exchangeable correlation structure.

Significance was accepted for p values <0.05. Data is obtained during inactive pill phase.

Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Significance was accepted for p values <0.05. Data is obtained during active pill phase.

Generalized estimating equation (GEE) with log link function and exchangeable correlation structure.

Significance was accepted for p values <0.05. Data is obtained during inactive pill phase.

Females ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) or on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold, and pregnancy.

Additional exclusion criteria for female participants: History of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training, or currently participating in competitive level sports.

Males: Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, and medications that lower seizure threshold.

Significance was accepted for p values <0.05.

Generalized linear model (GLM) with log link function and exchangeable correlation structure.

Females: ages 18-39 years, who are eumenorrheic (regular monthly cycles of 24-35 days) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, history of menstrual dysfunction (primary or secondary amenorrhea, oligomenorrhea, anovulatory cycles, polycystic ovarian disease), current pregnancy, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Females: ages 18-39 years, who are on a stable hormonal contraceptive regimen for 6 months (oral, transdermal or vaginal) and moderately active. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, started or stopped taking oral contraceptives within the previous 6 months, participate in high impact endurance training (i.e. pre-marathon training, body building), or currently participating in competitive level sports.

Ages 18-39. Exclusion criteria: History of musculoskeletal or orthopedic injury of the spine, hip, knee, ankle or foot, history of neurological injury of the peripheral or central nervous system, history of disordered eating, of a connective tissue disorder (Marfan's syndrome, Ehlers-Danlos disease), history of or current diabetes, pacemaker, metal implants in the head region, history of epilepsy or seizures, skull fractures or skull deficits, concussion within the last 6 months, unexplained recurring headaches, medications that lower seizure threshold.

Significance was accepted for p values <0.05. Data is obtained during follicular phase.

Generalized estimating equation (GEE) with log link function and exchangeable correlation structure.

Significance was accepted for p values <0.05. Data is obtained during luteal phase.