Andrew Cornwell

Acute effects of stretching on the neuromechanical properties of the triceps surae muscle complex.

Abstract. Previous research has shown that an acute bout of passive muscle stretching can diminish performance in certain movements where success is a function of maximal force and/or power output. Two possible mechanisms that might account for such findings are a change in active musculotendinous stiffness and a depression of muscle activation. To investigate the likelihood of these two mechanisms contributing to a post-stretch reduction in performance, we examined the acute effects of stretching on the active stiffness and muscle activation of the triceps surae muscle group during maximal single-joint jumps with movement restricted to the ankle joint. Ten males performed both static (SJ) and countermovement (CMJ) jumps before and after passively stretching the triceps surae. Electrical activity of the triceps surae during each jump was determined by integrating electromyographic recordings (IEMG) over the course of the movement. Triceps surae musculotendinous stiffness was calculated before and after stretching using a technique developed by Cavagna (1970). Following stretching, a significant decrease [mean (SD) 7.4 (1.9)%; P<0.05] in jump height for the CMJ occurred, but for the SJ, no significant (P>0.05) change in jump height was found. A small but significant decrease [2.8 (1.24)%; P<0.05] in stiffness was noted, but the magnitude of this change was probably not sufficient for it to have been a major factor underlying the decline in CMJ performance. Paradoxically, after stretching, the SJ exhibited a significant (P<0.05) decrease in IEMG, but the IEMG for the CMJ remained unchanged (P>0.05). It appears that an acute bout of stretching can impact negatively upon the performance of a single-joint CMJ, but it is unlikely that the mechanism responsible is a depression of muscle activation or a change in musculotendinous stiffness.

Inhibition of Maximal Voluntary Isometric Torque Production by Acute Stretching is Joint-Angle Specific

lthough stretching exercises that enhance flexibility A are regularly included in the training programs and pre-event warm-up activities of most athletes, research suggests that preexercise stretching could negatively impact the performance of skills for which success is related to maximal force output. Wilson, Murphy, and Pryor (1994) suggested that a stifFmusculotendinous system allows for an improved force production by the contractile component and provided evidence to support this suggestion by demonstrating that concentric performance in the bench press was significantly related to musculotendinous stiffness. The findings of Wilson et al. (1994), coupled with the results of several studies (Magnusson, Simonsen, Aagaard, & Kjaer, 1996; Rosenbaum & Hennig, 1995; Taylor, Dalton, Seaber, & Garrett, 1990), indicating that the musculotendinous unit becomes less stiff as a result of acute stretching, lead Kokkonen, Nelson, & Cornwell (1998) to investigate the effect of acute stretching on knee extension and knee flexion onerepetition maximum (IRM) lifts. Kokkonen et al. (1998) reported that a regimen of acute stretching inhibited the one-repetition maximum lift (IRM) of both knee extension and knee flexion. Kokkonen et al. (1998), however, could only speculate about the mechanisms responsible for this phenomenon. One speculated mechanism was derived from a Wilson et al. (1994) supposition that the lesser force pro-

Chronic stretching and running economy

Research demonstrates an inverse relationship between the range of motion of selected joint movements (flexibility) and running economy. Since stretching exercises have been shown to increase joint range of motion, stretching exercises may be contraindicated for endurance running performance. Hence, this study investigated the influence of a 10‐week program of stretching exercises on the oxygen costs of a 10 min sub‐maximal (approx. 70% peak VO2) treadmill run. Thirty‐two (16 female, 16 male) physically active, treadmill accommodated, college students participated in the study. All participants maintained their current activity level, with half the participants (8 female, 8 male) adding a 40 min, 3 days per week session of thigh and calf muscle stretching exercises. After 10 weeks, the stretching group (STR) exhibited a significant (P<0.05) increase (3.1±2.2 cm) in the sit‐and‐reach, while the non‐stretching group (CON) experienced no significant (P>0.05) change (0.0±0.4 cm). However, neither the STR nor the CON exhibited a significant (P>0.05) change in the O2 cost for the submaximal run. It is concluded, therefore, that a chronic stretching program does not necessarily negatively influence running economy.

Effects of Aerobic Exercise on Lipid-Effector Molecules of the Innate Immune Response

INTRODUCTION Consistent, moderate-to-vigorous-intensity exercise has been associated with a lower risk of upper respiratory tract infection (URI). However, the molecular basis for this apparent protection has not yet been fully resolved. Host-derived lipids such as cholesteryl esters (CE) have emerged as important effector molecules of innate defense against infections. Here, we compared antimicrobial CE in nasal fluid before and after moderate-to-vigorous exercise between active and inactive subjects. METHODS Nasal fluid was collected from 14 healthy, recreationally active subjects (32 ± 11 yr, 7 men and 7 women) and 14 healthy, inactive subjects (25 ± 3 yr, 7 men and 7 women) before and after treadmill exercise at 70% heart rate reserve. Nasal fluid was analyzed for lysozyme, cholesteryl linoleate (CL), cholesteryl arachidonate (CA), and albumin (Alb) concentrations. RESULTS Baseline concentrations (mean ± SEM, inactive vs active) of lysozyme (117.7 ± 31.1 vs 122.9 ± 15.5 μg·mL), CL + CA (15.3 ± 1.8 vs 26.2 ± 10.05 μg·mL), and Alb (156.6 ± 54.5 vs 126.9 ± 32.8 μg·mL) were similar to previously reported levels and did not differ significantly between study groups. However, postexercise, CL + CA concentration was significantly lower in inactive compared with active subjects (7.8 ± 1.5 vs 20.1 ± 4.8 μg·mL, P = 0.036) dropping below the antimicrobial effective range. Once adjusted to Alb concentrations, the changes were no longer significant, suggesting that plasma transudation accounted for the increased CA + CL concentration postexercise in the active group relative to the inactive group. CONCLUSIONS Moderate-to-vigorous aerobic exercise acutely decreases the antimicrobial CE response in inactive subjects but does not modify baseline levels of CE between active and inactive subjects. This suggests that compared with active individuals, inactive individuals may be at greater risk for upper respiratory tract infection immediately postexercise.