When you perform weightlifting, your body makes new proteins within your muscle. These new proteins can increase the size of the fibers within your muscle to make your muscle larger, a process called hypertrophy. The common convention surrounding gains in muscle mass and strength are that higher-loads (i.e. heavier weights) used for fewer repetitions are better for increasing strength and lower-loads (i.e. lighter weights) used for higher repetitions are better for increasing muscle mass. However, recent research has found that when higher- and lower-loads are used when participants exercise until volitional fatigue (i.e. cannot perform another repetition), muscle mass and strength increases are similar regardless of using a higher- or lower-load. Many of these studies have examined this effect in males with fewer studies examining the effects of higher- and lower-load training in females when assessing changes in muscle mass, strength, and muscle endurance.

Further, it has been shown that there is substantial individual variation in response to resistance exercise training where individuals can be broadly categorized as higher- or lower-responders to resistance exercise training. This study aims to explore how the muscle mass, strength, and muscle endurance of females are impacted by both higher- and lower-loads while also exploring how individuals may respond to the training interventions.

The study will be a total of 12 weeks in total duration. Weeks 1 and 12 will include testing assessments of skeletal muscle mass, muscle strength, and muscle endurance. Weeks 2-11 will be comprised of the resistance training intervention wherein participants will train thrice weekly at the Chan Gunn Pavilion research laboratory at the University of British Columbia.

Resistance training sessions will include unilateral knee extensions and unilateral dumbbell bicep preacher curls with each being performed for three sets. Limbs assigned to train with higher-loads will perform between 8-12 repetitions per set and limbs assigned to train with lower-loads will perform between 20-25 repetitions per set. Participants will rest 90 seconds between sets and 120 seconds between exercises. Each exercise will be performed in its entirety before moving on to the next.

Participants will also be supplemented with whey protein which will be ingested twice daily during the resistance training phase.

Inclusion Criteria:

1. Female
2. 18-30 years of age
3. Can fluently read and write in English
4. Able to commit to three training sessions per week for a continuous 10-week period as well as testing one week before and one week after this 10-week training period
5. All "No" answers on the Canadian Society for Exercise Physiology Get Active questionnaire or doctors' approval to participate

Exclusion Criteria:

1. Allergic to dairy products or are lactose-intolerant (participants will be supplemented with whey protein twice daily for the 10-week training period)
2. Allergic to any of the following ingredients which are present in the whey protein concentrate supplement: Bos taurus - Milk, Cocoa, Natural and Artificial Flavours, Xanthan Gum, Sucralose, Non-genetically modified organism Sunflower Lecithin
3. Any major uncontrolled cardiovascular, muscular, metabolic, and/or neurological disorders
4. Lung or kidney disease
5. Medical conditions impacting on their ability to undertake strenuous physical activity
6. Regular use of any mental health medications that may lead to excessive weight gain (selective serotonin reuptake inhibitors, second generation antipsychotics, antiepileptic drugs)
7. Participated in consistent resistance exercise training more than twice per month in the previous 12 months
8. Participated in consistent vigorous aerobic training more than twice per week in the previous 12 months
9. Significant gain or loss of body mass in the past 6 months (greater than 2 kg)
10. Current smoker
11. BMI less than 18 or over 30

A plan has not yet been made to make individual participant data available to other researchers