Recent research suggests that performing resistance exercise training with relatively light loads is equally as effective at increasing muscle mass and muscle strength as performing resistance exercise training with relatively heavy loads. Whether or not performing resistance exercise with relatively heavy loads or light loads is equally as effective between the upper- and lower-body within the same individual has never been investigated. Given the substantial individual variance in resistance exercise training-induced changes in muscle mass and strength, this study is designed to quantify the relative influence that extrinsic training variables (e.g., load), as opposed to intrinsic muscle-based predisposition, has on resistance training-induced changes in muscle mass and muscle strength.

Each participant will come to the Exercise Metabolism Research Laboratory gym three times per week for 10 weeks to perform lower- and upper-body resistance exercise training with both relatively heavy- (~80% one repetition maximum [1RM]) and light- (~40 %1RM) loads. One arm and one leg will be randomized to lift with relatively heavy loads such that the other arm and leg will be randomized to lift with relatively light loads. Each workout will be supervised by a study investigator.

The time commitment of this study is 12 weeks (including pre- and post-study testing). Each workout to take 30 minutes and, with testing days included, the investigators foresee a total time commitment of 41 hours, or just under three and half hours per week.

The pre- and post-study measurements include muscle biopsies, dual x-ray absorptiometry scans, ultrasonography scans, 1RM assessment, and maximum voluntary contraction assessment. The muscle biopsies will be taken from each of the participant's vastus lateralis to assess muscle fibre cross sectional area in both legs during the beginning (four biopsies) and end (four biopsies) of the intervention. The dual x-ray absorptiometry scans are used to assess body composition and will be done pre- and post-intervention. The ultrasonography scans will be used to assess biceps brachii and vastus laterals thickness and cross sectional area. The ultrasound scans will be assessed during the beginning (four scans) and end (four scans) of the intervention. The 1RM assessment will include 1RM testing on a knee extension machine and biceps curl machine and will be done at the beginning and end of the intervention. The maximum voluntary contraction assessment will be performed on a System 3 Biodex Dynamometer (Shirley, NY, USA), which is an immovable machine that the participants contract against to measure their peak force. The maximum voluntary contractions will be recorded three times: twice at the beginning of the intervention and once at the end of the intervention.

Inclusion Criteria:

• Be between the ages of 18-30 years (inclusive)
• Be able to maintain a habitual diet and perform resistance exercise three times per week throughout the trial
• Be in general good health (assessed by Get Active Questionnaire)
• Understand the study procedures and sign this form providing informed consent to participate in the study.

Exclusion Criteria:

• Use of tobacco or related products
• A history of neuromuscular problems or muscle and/or bone wasting diseases
• Any acute or chronic illness; cardiac, pulmonary, liver, or kidney abnormalities; insulin- or non-insulin-dependent diabetes or other metabolic disorders (all ascertained through medical questionnaires)
• Use of medications known to affect protein metabolism (i.e. corticosteroids, non-steroidal anti-inflammatory drugs (prescription use or daily use of over the counter medication), or prescription strength acne medications)

No individual participant data will be made available to other researchers

The histochemistry and ultrasonography were analyzed by blinded study investigators