TIME COURSE OF STRESS RELAXATION WITH REPETITIVE STRETCHING OF HUMAN PLANTARFLEXORS

Abstract

1445 The purpose of this study was to monitor the stress relaxation response to repeated maximum passive stretching (PSmax) of the ankle plantarflexors. Ten university students (6 men, 4 women) underwent 25 min of cyclical, PSmax (10 stretches [S1-S10] over 25 min, 15 s rest between stretches) to a maximum dorsiflexion position (Dmax) each stretch. Soleus EMG confirmed that each stretch was passive. Dmax joint angle, peak passive torque (PTpeak), and passive torque in Dmax was observed during each 2 min stretch, and passive torque decay (PTd) for the intervals from 0 to 15 s (I1), 15 to 30 s (I2), 30 to 45 s (I3), and 105 to 120 s (IE) was calculated. Dmax increased significantly by S2 (P<0.005) and from S2 to S3 (P<0.05) so that 59%(3.4 °) of a total 5.8 ° increase in Dmax over ten stretches(P<0.005), had occured by S3 (P<0.005). PTpeak increased 12% from S1 to S8 (P=0.06). Total PTd was greater in S1 (P<0.005) than S2-S10. Greater PTd was observed in I1 (P<0.005) than I2, I3, and IE of any single stretch so that 45% of PTd in a 2 min stretch, occurs in the first 15s. Greater PTd was observed in I1 of S1 compared to I1 of all other stretches (P<0.005). These data indicate that a significant viscoelastic stress relaxation response occurs within the first 15s of a single stretch and within the first two stretches of a ten stretch protocol. Tissue creep, and increased stretch tolerance, likely allow for further responses beyond the early viscoelastic stress relaxation.