Changes in Quadriceps Motoneuron Pool Excitability due to Static Stretch and/or Explosive Contraction

Abstract

PURPOSE: To observe how static stretch and/or explosive contraction (vertical jump) changes quadriceps motoneuron pool excitability (MNPE). METHODS: Fifteen healthy people (13 males and 2 females) completed four data collection sessions on separate days with a 48-hour interval between sessions. A 4 (condition) × 3 (time) cross-over randomised controlled laboratory study was performed. Conditions were A) stretching and jumping, B) control (no stretching) and jumping, C) stretching and control (no jumping), and D) control (no stretching and jumping). Thomas test was used to stretch both quadriceps (30-s × 3 for each quadriceps). For jumping, two-legged maximal vertical jumps using lower-extremity pre-stretch and double-arm swinging were performed (assessed by Vertec: 3 trials with a-30 s rest interval). To assess quadriceps MNPE, the right side of vastus medialis peak Hoffmann reflexes normalised by peak motor response were recorded at baseline, 0-min post-condition, and 20-min post-condition. For the conditions including the jumping task, jump heights were also recorded after measurements of MNPE at each time point. To test condition effects over time, mixed model analysis of variances were performed and between-time effect sizes (ES) were calculated. RESULTS: Quadriceps MNPE did not change among four conditions at any time point (F6,154=1.71, p=0.12). There was a trend that quadriceps MNPE at 0-min post-condition, as compared to the baseline values, was reduced under the condition A (5%, ES=0.46) and C (8%, ES=0.43), and increased under the condition B (10%, ES=0.66). An increased quadriceps MNPE under the condition B appeared to be maintained until the 20-min post-condition measurement (8%, ES=0.52). Jump heights did not change among two conditions (A and B) at any time point (F2,70=2.14, p=0.13). Jump heights between-time ES were very small (<0.1 for all values). CONCLUSIONS: Our data suggest that (1) static stretch may reduce MNPE, (2) explosive contraction may increase MNPE for 20-min, (3) a combination of static stretch and explosive contraction may decrease MNPE, (4) three sets of 30-s stretch does not acutely affect explosive performance, and (5) changes in MNPE minimally influence explosive performance. This study was funded by Yonsei Institute of Sports Science & Exercise Medicine.