The goal of this clinical trial was to compare to different types of high-intensity interval training in young, healthy females. The main questions were: Will changes in body composition differ between the two interventions? Will changes in endurance and muscle performance differ between the two interventions? Participants were randomized to 8 weeks of high-intensity interval training involving body weight, plyometric exercises or cycling only. Researchers compared changes in endurance performance, body composition, and muscle performance to determine if there were differences between groups.

The purpose of this study was to compare the effects of plyometric- and cycle-oriented high-intensity interval training on body composition, aerobic capacity, and skeletal muscle size, quality, and function in recreationally trained females. Young (21.7 ± 3.1 yrs), recreationally active females were randomly assigned to 8 weeks of twice weekly plyometric (n = 15) or cycling (n = 15) high-intensity interval training. The plyometric-oriented Les Mills BODYATTACK program was used for the plyometric group whereas Les Mills SPRINT, which exclusively involves stationary cycling, represented the cycling group. Both protocols involved alternating high-intensity and recovery intervals, and participants were consistently instructed to give maximal effort during the 'work' periods.

The 30 min plyometric routines included four blocks of high-intensity exercise intervals. The 'work' portions consisted of the following exercises: high-knee runs, plyometric lunges, jumping jacks, squat jumps, burpees, and speed-agility patterns. The recovery periods consisted of complete rest (transitioning between exercises), a light jog, or a low impact stepping motion. On average, participants were instructed to give maximal effort for 1-2 min, with recovery intervals of 15-45 sec. Four separate routines were used throughout the duration of the study, keeping one routine per week; participants completed each routine a total of 4 times within a session.

The 30 min cycling routines were performed on upright stationary bikes (Schwinn, AC Performance, Chicago, IL). Protocols involved 'work' ranging from 20-80 sec with recovery intervals between 10-60 sec. Recovery intervals consisted of complete rest on bike or particularly slow cycling. Resistance and cycling speed were relatively variable across sessions, with some intervals of higher resistance and lower speed and others involving lower resistance and higher speed (e.g., >120 RPMs). The same four workouts were used throughout the duration of the study alternating each week.

Body composition (4-compartment model), VO2peak, countermovement jump performance, muscle size and echo intensity (muscle quality) as well as strength and power of the knee extensors and plantar flexors were measured before and after training. Body composition testing was completing using dual-energy x-ray absorpiometry, air displacement plethysmogrphay, and bioeletrical impedance. VO2peak was measured using a standardized maximal exercise test on a treadmill. Countermovement jump height and power was recorded with participants performing jumps on a force plate. Muscle size and quality were determined using non-invasive ultrasonography. Finally, serum growth hormone responses to the VO2peak test were measured before and after the protocols.

Inclusion Criteria:

• Between 18-35 years of age
• Female
• Currently participating in 2-4 days of structured exercise for 30-75 minutes for the last 6 months

Exclusion Criteria:

• Currently participating in these exercise formats (2x/week within last 3 months)
• Engaging in high intensity interval training for more than 30 min/week
• Have diagnosed disorders/diseases in the following: cardiovascular, pulmonary, immunological, or metabolic
• Current musculoskeletal injuries
• Pregnant or think you may be pregnant
• Currently taking any non-steroidal anti-inflammatory drug(s) or steroidal drug(s)
• Currently a smoker or has consistently smoked within the last year
• Has a positive written or verbal pre-study drug screen including alcohol (more than 7 drinks/week), THC/cannabinoids, amphetamines, benzodiazepines, cocaine, opioids, phencyclidine, barbiturates, cotinine.
• Currently taking any medication that will significantly affect your heart rate response to exercise
• If you miss four or more classes, you will be excluded from the study

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