UBC Theses and Dissertations
Muscle and tendon characteristics after six weeks of overloaded stretch training Simpson, Carey Lynn
Stretching is used to maintain mobility, increase range of motion and rehabilitate muscles after injury. It is rarely suggested as a modality for increasing muscle size in humans, although animal studies have reported stretch induced muscle hypertrophy. The purpose of this study was to examine whether six weeks of passive stretching of the plantar flexors would stimulate muscle hypertrophy. The first hypothesis was that stretch training would induce muscle hypertrophy, increase fascicle lengths and decrease pennation angles of the medial and lateral gastrocnemius without altering the Achilles tendon, but changes in muscle architecture would be non-uniform between the gastrocnemii. The second hypothesis was stretch training would decrease maximal force and electromyography (EMG) activity of the plantar flexors through shifting the length tension relationship without changing voluntary activation or reflex activity. Eleven males stretched the non-dominant plantar flexors for six consecutive weeks by using a leg press to passively load the ball of the foot. The load was 20% of the baseline maximal voluntary contraction. EMG was monitored on-line for each session to ensure the subject was stretching and not contracting, which would be indicated by muscle activity. At week zero, three, six and one week after the completion of stretching ultrasound was used to measure muscle architectural and tendon changes. Force, EMG, twitch interpolation, reflex activity, contractile properties and body anthropometry were also measured. Both hypotheses were supported. Muscle depth increased 10.3% (p=0.04) by week three in the stretched leg with a 25% (p<0.001) increase in the length of the muscle fascicles in the muscle tendon junction, and 5.1% (p=0.01) increase in the fascicles of the muscle belly (n=3600). The pennation angle (n=3600) decreased (p=0.02) with no change in the tendon (p=0.95). Muscle force decreased 10.5% (p=0.008) at week six, with a reduction in EMG amplitude (p<0.001) and no change in voluntary activation (95.48% ± 0.92, p>0.05) or reflex activity (p>0.05). These data indicated six weeks of overloaded stretch training of the plantar flexors stimulated muscle hypertrophy but also caused significant reductions in force through an alteration in the length tension relationship.
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