Matthew D. Fliss’ MSc Thesis Defence

Title: The Effects of Higher- And Lower-Load Resistance Exercise Training on Leg and Arm Skeletal Muscle Mass in Healthy Young Adult Females: A Randomized Equivalence Trial

Thesis Supervisor: Dr. Cameron Mitchell
Committee members: Dr. Bill Sheel, Dr. Kristin Campbell
Chair: Dr. Michael Koehle

Abstract: Resistance exercise training (RET) is a potent stimulus for skeletal muscle hypertrophy. Moderate/heavier loads are traditionally more effective for inducing muscle growth compared to lighter loads, but recent research has demonstrated that lighter load (LL) RET can lead to similar muscle hypertrophy as higher load (HL) RET when individuals train to volitional fatigue. While this result has been consistently shown in males, there is limited and conflicting results in similar studies using female participants. The primary aim of this study was to compare the muscle hypertrophic response to HL and LL RET in the upper and lower body of young adult females. The secondary aims of this study was to examine the strength, local muscle endurance, and muscle architecture adaptations in response to HL and LL RET in the upper and lower body of young adult females. The study used a randomized repeated measures within-participant design wherein each participant had one arm and leg assigned to train with HL and the other arm and leg assigned to train with LL. Participants performed thrice weekly training sessions over a 10-week training period where unilateral knee extension and unilateral dumbbell bicep preacher curls were performed for three sets each. Biceps brachii thickness increased following both LL and HL RET (∆LL = 0.3±0.4 cm, ∆HL = 0.2±0.4 cm, Interaction P = 0.12), but upper arm lean mass only increased following LL RET (∆LL = 0.1±0.2 kg, ∆HL = 0.04±0.2 kg, Interaction P = 0.02). Neither HL nor LL RET induced an increase in any measure of lower body muscle size. Therefore, LL RET induces a greater training volume compared to HL RET in the elbow flexors due to similar absolute loads used during training. In the lower body, training volume must be considered as neither loading condition reached the necessary total training volume required to induce measurable muscle growth.