Arnold G. Nelson

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.

Acute effects of passive muscle stretching on sprint performance

The results of previous research have shown that passive muscle stretching can diminish the peak force output of subsequent maximal isometric, concentric and stretch-shortening contractions. The aim of this study was to establish whether the deleterious effects of passive stretching seen in laboratory settings would be manifest in a performance setting. Sixteen members (11 males, 5 females) of a Division I NCAA track athletics team performed electronically timed 20 m sprints with and without prior stretching of the legs. The experiment was done as part of each athletes Monday work-out programme. Four different stretch protocols were used, with each protocol completed on a different day. Hence, the test period lasted 4 weeks. The four stretching protocols were no-stretch of either leg (NS), both legs stretched (BS), forward leg in the starting position stretched (FS) and rear leg in the starting position stretched (RS). Three stretching exercises (hamstring stretch, quadriceps stretch, calf stretch) were used for the BS, FS and RS protocols. Each stretching exercise was performed four times, and each time the stretch was maintained for 30 s. The BS, FS and RS protocols induced a significant (P  < 0.05) increase (∼0.04 s) in the 20 m time. Thus, it appears that pre-event stretching might negatively impact the performance of high-power short-term exercise.

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-

Acute muscle stretching inhibits muscle strength endurance performance.

Since strength and muscular strength endurance are linked, it is possible that the inhibitory influence that prior stretching has on strength can also extend to the reduction of muscle strength endurance. To date, however, studies measuring muscle strength endurance poststretching have been criticized because of problems with their reliability. The purpose of this study was twofold: both the muscle strength endurance performance after acute static stretching exercises and the repeatability of those differences were measured. Two separate experiments were conducted. In experiment 1, the knee-flexion muscle strength endurance exercise was measured by exercise performed at 60 and 40% of body weight following either a no-stretching or stretching regimen. In experiment 2, using a test-retest protocol, a knee-flexion muscle strength endurance exercise was performed at 50% body weight on 4 different days, with 2 tests following a nostretching regimen (RNS) and 2 tests following a stretching regimen (RST). For experiment 1, when exercise was performed at 60% of body weight, stretching significantly (p < 0.05) reduced muscle strength endurance by 24%, and at 40% of body weight, it was reduced by 9%. For experiment 2, reliability was high (RNS, intraclass correlation = 0.94; RST, intraclass correlation = 0.97). Stretching also significantly (p < 0.05) reduced muscle strength endurance by 28%. Therefore, it is recommended that heavy static stretching exercises of a muscle group be avoided prior to any performances requiring maximal muscle strength endurance.

Acute Ballistic Muscle Stretching Inhibits Maximal Strength Performance

In the December 1998 issue of Research Quarterly for Exercise and Sport, we presented data showing that acute static stretching of the hip, thigh, and calf muscles before the performance of a one-repetition maximum lift (lRM) resulted in a decreased IRM for both knee flexion and knee extension (Kokkonen, Nelson, & Cornwell, 1998). Since then, we have had the opportunity to engage in dialogue with many individuals who were interested in discussing the implications and mechanisms that accompanied our finding. The foremost question has dealt with the type of stretching activity used in the study. Because static stretching was used, many people asked if the negative impact of stretching was present following ballistic stretching. Unfortunately, we could not answer this question with any precision. In the Kokkonen et al. (1998) study, the issue of ballistic stretching had been avoided, because most exercise physiology textbooks recommend against doing ballistic stretching (see deVries & Housh, 1994; Foss & Keteyian, 1998; Plowman & Smith, 1997; Powers & Howley, 2001; Robergs & Roberts, 1997). The basis behind these recommendations is that ballistic stretching increases the chance of muscle injury, because the athlete is trying to lengthen the muscle while the myotatic reflex is contract-

Static stretching impairs sprint performance in collegiate track and field athletes

Previous research has shown that static stretching (SS) can diminish the peak force output of stretch-shortening cycle actions while performing a dynamic warm-up (DW) protocol has been shown to enhance performance in similar activities. The purpose of this study was to establish whether the deleterious effects of SS would wash out the performance enhancements obtained from the DW. Eleven males and 11 females, who were athletes of a NCAA Division I track team, performed a DW followed with either a SS or rest (NS) condition. After warm-up was completed, three 40 m sprints were performed to investigate the effects of the SS condition on sprint performance when preceded by DW. Time(s) were obtained from timing gates placed at 0, 20, and 40 m respectively. Testing was conducted over 2 days with a 1 week washout period. Testing order was balanced to eliminate possible order effect. Time for the NS versus the SS group was significantly faster for the second 20 m with a time of 2.41 versus 2.38 seconds (P ≤ .05), and for the entire 40 m with a time of 5.6 ± 0.4 versus 5.7 ± 0.4 seconds (P ≤ .05). The results of this study suggest that performing a SS protocol following a DW will inhibit sprint performance in collegiate athletes.

Creatine Supplementation Enhances Intermittent Work Performance

To determine the impact of creatine supplementation on high-intensity, intermittent work, 18 participants each performed 2 sets of 4 different work bouts to exhaustion. For 5 days prior to the first set of work bouts, all participants received a placebo (5 g of calcium chloride daily). For the second set of work bouts, 9 participants again received the placebo, while the other 9 received creatine supplementation (18.75 g creatine monohydrate daily for 5 days prior to and 2.25 g creatine daily during testing). The four work bouts in each set consisted of cycling to exhaustion at 150% peak oxygen uptake (VO2peak) either nonstop (A), intermittently for either 60-s work/120-s rest periods (B), 20-s work/40-s rest (C), or 10-s work/20-s rest (D). Creatine supplementation significantly increased (p < .01) the total work time of all bouts. Protocol D showed the greatest increase (> 100%); C increased 61.9%; B increased 61.0%; and A increased 23.5%. These results demonstrate that creatine supplementation significantly extends ones capacity to maintain a specific level of high-intensity, intermittent exercise.

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 caffeine ingestion on endurance racing in heat and humidity.

A hot and humid environment can be detrimental to race performance. Caffeine, on the other hand, has been shown to be an ergogenic aid for improving endurance performance. To examine the influence of caffeine ingestion on race performance during high heat stress, seven endurance trained competitive road racers aged between 23 and 51 years (five men, two women) performed three maximal effort 21-km road races outdoors in hot and humid conditions. The caffeine dose, randomly assigned in a double-blind fashion, consisted of either 0, 5, or 9 mg · kg−1 body mass. During each run, the subjects were allowed to drink waterad libitum at each 5-km point. Blood samples were obtained immediately before and after each run and analysed for changes in concentrations of Na+, K+, glucose, lactate, and hematocrit. Pre and postrun data were also collected for body mass and tympanic membrane temperature. Race times were not significantly different among the races or caffeine doses, with the average times within 1.1% of each other. In addition, none of the other variables measured varied significantly among the races or caffeine doses. In summary, caffeine intake did not affect race performance. Therefore it was concluded from our study that caffeine is not of ergogenic benefit in endurance races during high heat stress.

Relationship between isometric and dynamic strength in recreationally trained men.

McGuigan, MR, Newton, MJ, Winchester, JB, and Nelson, AG. Relationship between isometric and dynamic strength in recreationally trained men. Strength Cond Res 24(9): 2570-2573, 2010-The purpose of this investigation was to examine the relationships between measures of maximal isometric force (peak force [PF]), rate of force development (RFD), vertical jump performance (VJ) and 1-repetition maximum (1RM) strength in recreationally trained men. The subjects in this study were 26 men ([mean ± SD]: age 22 ± 1 years; height 175 ± 7 cm; mass 90 ± 10 kg). They were tested for PF using the isometric midthigh pull exercise. The 1RM for the squat and bench press exercise were determined as a measure of dynamic strength. Explosive strength was measured as RFD from the isometric force-time curve. Correlations between the variables were calculated using Pearson product moment correlation coefficient. There was a nearly perfect correlation between measures of PF and 1RM squat (r = 0.97, p < 0.05) and 1RM bench press (r = 0.99, p < 0.05). The correlations were very strong between VJ and PF (r = 0.72, p < 0.05) and 1RM bench press (r = 0.70, p < 0.05). There were also strong correlations between VJ and 1RM squat (r = 0.69, p < 0.05). There were no significant correlations with RFD. The results showed that isometric maximum strength determined during the isometric midthigh pull test correlated well with 1RM and VJ testing. However, RFD measured during the same test did not appear to correlate as well with other measures. The isometric midthigh pull provides an efficient method for assessing strength in recreationally trained individuals. Practioners wishing to obtain performance data related to maximum strength may wish to consider isometric testing as a less time intensive method of testing.