Purpose: The purpose of the present study was to examine the effects of constant-angle (CA) and constant-torque (CT) stretching of the leg flexors on peak torque (PT), EMGRMS at PT, passive range of motion (PROM), passive torque (PASTQ), and musculotendinous stiffness (MTS). Methods: Seventeen healthy men (mean ± SD: age = 21.4 ± 2.4 yr) performed a PROM assessment and an isometric maximal voluntary contraction of the leg flexors at a knee joint angle of 80° below full leg extension before and after 8 min of CA and CT stretching. PASTQ and MTS were measured at three common joint angles for before and after assessments. Results: PT decreased (mean ± SE = 5.63 ± 1.65 N·m) (P = 0.004), and EMGRMS was unchanged (P > 0.05) from before to after stretching for both treatments. PROM increased (5.00° ± 1.03°) and PASTQ decreased at all three angles before to after stretching (angle 1 = 5.03 ± 4.52 N·m, angle 2 = 6.30 ± 5.88 N·m, angle 3 = 6.68 ± 6.33 N·m) for both treatments (P = 0.001). In addition, MTS decreased at all three angles (angle 1 = 0.23 ± 0.29 N·m·°-1, angle 2 = 0.26 ± 0.35 N·m·°-1, angle 3 = 0.28± 0.44 N·m·°-1) after the CT stretching treatment (P < 0.005); however, MTS was unchanged after CA stretching (P > 0.05). Conclusions: PT, EMGRMS, PROM, and PASTQ changed in a similar manner after stretching treatments; however, only CT stretching resulted in a decrease in MTS. Therefore, if the primary goal of the stretching routine is to decrease MTS, these results suggest that CT stretching (constant pressure) may be more appropriate than a stretch held at a constant muscle length (CA stretching).
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