Sex differences in stretch-induced hypertrophy, maximal strength and flexibility gains.
Level 3 - non-randomized controlled study
Prospective within-subject controlled intervention study without reported randomization
PubMed 36685189 · doi:10.3389/fphys.2022.1078301
What was done
Fifty-five healthy, active participants (28 men, 27 women) underwent a 6-week intervention consisting of daily 1-hour unilateral static stretch training of the plantar flexors using a calf-muscle stretching device. Maximal strength (MSt) and range of motion (ROM) were evaluated with the knee joint both extended and flexed, and muscle thickness (MTh) was measured via ultrasound in the medial and lateral heads of the gastrocnemius.
What was found
Considering both sexes and both legs, significant pre-to-post improvements were observed: - Maximal strength increased by 6% to 15% (p < .001 to .049, d = 0.45 to 1.09). - Range of motion increased by 6% to 21% (p < .001 to .037, d = 0.47 to 1.38). - Muscle thickness increased by 4% to 14% (p < .001 to .005, d = 0.46 to 0.72). Men achieved significantly greater increases in MSt, MTh, and ROM than women. In both sexes, adaptations in MSt and ROM were greater with an extended knee joint, and MTh gains were larger in the medial gastrocnemius head (p < .001 to .047). Relative MSt increases similarly favored men (p < .001 to .036, d = 0.48 to 1.03).
Why it matters
This study demonstrates that prolonged passive static stretch can induce skeletal muscle hypertrophy and strength gains in humans, while showing that men experience greater structural and functional adaptations than women from identical stretching protocols.
Limits
The 1-hour daily stretching volume is time-intensive and impractical for most clinical or athletic regimens. The abstract does not report randomization, blinding, long-term retention of adaptations, or systemic physiological mechanisms driving the observed sex differences.
Cited by
- supports Stretching the calf muscle for one hour a day using a stretching boot resulted in approximately 15% muscle growth in muscle thickness.