Unilateral plantar flexors static-stretching effects on ipsilateral and contralateral jump measures.

Author:da Silva, Josinaldo Jarbas
Position:Research article - Report
 
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Introduction

Several articles have reported non-local (e.g. upper versus lower body) or cross-over (contralateral muscle) effects with an exercised muscle affecting the performance of a non-exercised muscle when monitoring fatigue (Doix et al., 2013; Rattey et al., 2006; Regueme et al., 2007; Todd et al., 2003), and force/power (Carroll et al., 2006; Farthing et al., 2005; Lee and Carroll, 2007; Sariyildiz et al., 2011; Shima et al., 2002). However, few articles have examined the cross-over effect after static-stretching (SS) (Nelson et al., 2012). Both differences (Cramer et al., 2004) and lack of differences (Avela et al., 1999; Cramer et al., 2006; Guissard and Duchateau, 2004) have been observed between limbs for force and range of motion (ROM), however there are no articles related to crossover effect with jumping tasks (power capacity). Cramer et al. (2004, 2006) exemplified this conflict with two studies that examined the effects of SS on isokinetic leg extension peak torque measures at two different velocities (2004 study: 60[degrees][s.sup.-1] and 240[degrees][s.sup.-1], 2006 study: 60[degrees][s.sup.-1] and 180[degrees][s.sup.-1]) in the stretched and non-stretched limbs of men and women. The earlier study with men showed that peak torque decreased following the SS in both limbs and at both velocities while the latter study with women reported no contralateral effects. Marchetti et al. (2014) demonstrated the effect of upper body stretching on lower body performance. They employed 10 upper body stretches of 30s duration at 70-90% of the point of discomfort and found impairments of both the propulsion duration and peak force of a maximal concentric jump but no effect on lower limb muscle activation. Avela (1999) analyzed the effect of prolonged and repeated passive stretching of the triceps surae muscle on reflex sensitivity. The results demonstrated a decrease of muscle function immediately after the protocol, however the non-stretched leg (control leg) demonstrated nonsignificant changes in the maximal voluntary contraction (MVC). Nelson, et al. (2012) analyzed 10-week stretching program (4 times for 30s, with 30s rest, 3 d x [wk.sup.-1]). The results indicated an increase in strength (1RM) for both legs (stretched and non-stretched limb), where the strength gain of the non-stretched leg was 56% of the stretched leg. Non-local muscle deficits and training adaptations suggest that SS-induced alterations are related to central nervous system mechanisms.

Several studies have reported deleterious effects of SS on different drop jump variables, such as jump height (Behm et al., 2001b; Behm and Chaouachi, 2011; Behm and Kibele, 2007; Rubini et al., 2007), contact time (Behm and Kibele, 2007; Rubini et al., 2007), and surface electromyography (sEMG) (Cornwell et al., 2002; Wallmann et al., 2005) with the stretched leg. These plyometric performance reductions can originate from neurophysiological (i.e. mechanoreceptors of the skin, muscle and joint proprioception), hormonal, cellular (structural changes such as titin), or mechanical (i.e. stiffness, torque-length characteristics) factors (Behm et al., 2001a; Behm and Chaouachi, 2011; Rubini et al., 2007), and in some studies, it might persist for over several hours post-stretch (Brandenburg et al., 2007; Fowles et al., 2000; Haddad et al., 2014; Power et al., 2004). Brandenburg et al. (2007) observed decreases immediately after SS on maximal height of the countermovement vertical jump, and it remained decreased during the 24 minute follow-up period. Power et al. (2004) demonstrated impairments of quadriceps force, and jump contact time from 1 to 120 minutes post-stretching. However, there are no studies that have examined the time course of SS effects on muscle pre-activation or time to peak force of the landing phase of the single-leg bounce drop jump (SBDJ). The landing phase is an important component of the jumping performance. Plyometric exercises that involve a rapid stretch-shortening cycle (SSC) involve both a preactivation (muscle activation before landing to increase the joint stiffness) and pre-stretch of the muscles that incorporate muscle reflex activity and the storage and release of elastic energy (Cappa and Behm, 2013). It is also unknown whether any SS-induced deficits with the stretched leg would be transferred to the contralateral leg.

Therefore, the purpose of the present study was to evaluate the acute effects of unilateral ankle plantar flexors SS on (1) the sEMG (integral EMG {IEMG}, [IEMG.sub.pre.activition]) and jump performance (jump height, total impulse, time to peak force, contact time) of nonstretched lower limbs during SBDJ tasks, and (2) time course and extent of sEMG (IEMG, [IEMG.sub.pre-activation]), passive ROM and jump performance (jump height, total impulse, time to peak force, contact time) of the stretched lower limb with healthy adult males. It was hypothesized that both the stretched and non-stretched contralateral limbs would experience impairments.

Methods

Subjects

Based on a statistical power analysis derived from the IEMG data from Marchetti et al. (2014), fifteen subjects would be necessary to achieve an alpha level of 0.05 and a power (1-[beta]) of 0.80. Therefore, 17 young, healthy, trained men (age: 24 [+ or -] 5 years, height: 1.74 [+ or -] 0.07 m, and weight: 77.3 [+ or -] 13.0 kg) were recruited to participate in this study. They had 3[+ or -]1 years of experience with resistance training, at least 3 times a week, regularly. The participants in the study had no previous surgery on the lower extremities (specifically in the ankle joint); no history of injury with residual symptoms (pain, "giving-away" sensations) in the lower limbs within the last year. This study was approved by the research ethics committee of the University (Protocol #74/12).

Procedures

This was a quazi-experimental, repeated measures study. Prior to the data collection, subjects were asked to identify the preferred leg for kicking a ball, which was then considered the dominant leg. Of the 17 subjects, 15 were right-leg dominant. The experimental protocol consisted of (1) a brief submaximal jumping warm-up for 5 minutes; (2) a pre-stretching evaluation (passive ROM and three trials of maximal single-leg jumping task for each lower limb); (3) ankle plantar flexors SS protocol (only for dominant lower limb); (4) immediate post-stretching evaluation (passive ROM and three trials of maximal single-leg jumping task) for both lower limbs; and (5) further post-stretching evaluation at 10 and 20 minutes only for the stretched lower limb (three trials of unilateral jumping task), considering the mechanical stress imposed by the static- stretching protocol only on that particular limb. Only the pre-stretching evaluations were randomized between legs and subjects. The order of testing used in the pre-test was then maintained for the post-test, and all measures were performed at the same hour of the day, between 9 AM and 12 PM.

Maximal single-leg jumping task (Single-leg Bounce drop jump, SBDJ): The SBDJ was performed before and after the unilateral ankle plantar flexors stretching protocol (only the dominant lower limb was stretched). The SBDJ is a jump technique where the subject jumps maximally as soon as possible after landing. The technique emphasizes the ankle plantar flexors and involves minimum knee flexion and minimum ground contact time. Subjects were instructed to perform the SBDJ fall from a 15cm step, and terminate the landing phase in a standing position with their arms crossed on the chest. Immediately upon contact with the force plate (landing phase), subjects were instructed to jump maximally with minimal contact time. Subjects were...

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