Joke Kokkonen

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-

Muscle glycogen supercompensation is enhanced by prior creatine supplementation

PURPOSE Recently, it was shown that glycogen supercompensation tended (P = 0.06) to be greater if creatine and glycogen were loaded simultaneously. Because the authors suggested that creatine loading increased cell volumes and, therefore, enhanced glycogen supercompensation, we decided to determine whether an enhanced glycogen supercompensation could be realized if the glycogen loading protocol was preceded by a 5-d creatine load. METHODS Twelve men (19-28 yr) performed two standard glycogen loading protocols interspersed with a standard creatine load of 20 g.d(-1) for 5 d. The vastus lateralis muscle was biopsied before and after each loading protocol. RESULTS The initial glycogen loading protocol showed a significant 4% increase (P < 0.05) in muscle glycogen (Delta upward arrow 164 +/- 87 mmol.kg(-1) d.m.), and no change (P > 0.05) in total muscle creatine. Biopsies pre- and post-creatine loading showed significant increases in total muscle creatine levels in both the left leg (Delta upward arrow 41.1 +/- 31.1 mmol.kg(-1) d.m.) and the right leg (Delta upward arrow 36.6 +/- 19.8 mmol.kg(-1) d.m.), with no change in either legs muscle glycogen content. After the final glycogen loading, a significant 53% increase in muscle glycogen (Delta upward arrow 241 +/- 150 mmol.kg-1 d.m.) was detected. Finally, the postcreatine load total glycogen content (694 +/- 156 mmol.kg(-1) d.m.) was significantly (P < 0.05) greater than the precreatine load total glycogen content (597 +/- 142 mmol.kg(-1) d.m.). CONCLUSION It is suggested that a muscles glycogen loading capacity is influenced by its initial levels of creatine and the accompanying alterations in cell volume.

Creatine supplementation alters the response to a graded cycle ergometer test.

Abstract To determine the effects of creatine supplementation on cardiorespiratory responses during a graded exercise test (GXT) 36 trained adults (20 male, 16 female; 21–27 years old) performed two maximal GXTs on a cycle ergometer. The first GXT was done in a non-supplemented condition, and the second GXT was done following 7 days of ingesting either 5 g creatine monohydrate, encased in gelatin capsules, four times daily (CS, 13 male, 6 female), or the same number of glucose capsules (PL, 7 male, 10 female). CS significantly (P < 0.05) improved total test time [pre-CS=1217 (240) s, mean (std. dev.) versus post-CS=1289 (215) s], while PL administration had no effect (P > 0.05) on total test time [pre-PL=1037 (181) s versus post-PL=1047 (172) s]. In addition, both oxygen consumption (V˙O2) and heart rate at the end of each of the first five GXT stages were significantly lower after CS, but were unchanged after PL. Moreover, the ventilatory threshold occurred at a significantly greater V˙O2 for CS [pre-CS=2.2 (0.4) l · min−1 or 66% of peak V˙O2 versus post-CS=2.6 (0.5) l · min−1 or 78% of peak V˙O2; pre-PL=2.6 (0.9) l · min−1 or 70% peak V˙O2 versus post-PL=2.6 (1.1) l · min−1 or 68% of peak V˙O2]. Neither CS nor PL had an effect on peak V˙O2 [pre-CS=3.4 (0.7) l · min−1 versus post-CS=3.3 (0.7) l · min−1; pre-PL=3.7 (1.1) l · min−1 versus post-PL=3.7 (1.1) l · min−1]. Apparently, CS can alter the contributions of the different metabolic systems during the initial stages of a GXT. Thus, the body is able to perform the sub-maximal workloads at a lower oxygen cost with a concomitant reduction in the work performed by the cardiovascular system.

Strength Inhibition Following An Acute Stretch Is Not Limited To Novice Stretchers

Flexibility (joint range of motion) is promoted as an important component of physical fitness (Pollock et al., 1998). It is widely conjectured that increasing flexibility will promote better performances and reduce the incidence of injury (Shellock & Prentice, 1985; Smith, 1994). Consequently, stretching exercises designed to enhance flexibility are regularly included in many athletes’ training programs and pre-event warm-up activities (Gleim & McHugh, 1997; Holcomb, 2000). Notwithstanding the widespread acceptance and use of stretching exercises as a major component of pre-event activities, the purported benefits of stretching on performance and injury prevention have been questioned in several review papers (Gleim & McHugh, 1997; Herbert & Gabriel, 2002; Knudson, 1999; Weldon & Hill, 2003.). In addition, recent research has established an adverse effect of acute static stretching on various different maximal performances. Pre-event stretching has demonstrated an inhibitory effect on maximal force or torque production (Avela, Kyrolainen, & Komi, 1999; Behm, Button, & Butt; 2001; Evetovich, Nauman, Conley, & Todd, 2003; Fowles, Sale, & MacDougall, 2000; Kokkonen, Nelson, & Cornwell, 1998; Nelson, Allen, Cornwell, & Kokkonen, 2001; Nelson, Guillory, Cornwell, & Kokkonen, 2001; Nelson & Kokkonen, 2001), vertical jump performance (Church, Wiggins, Moode, & Crist, 2001; Cornwell, Nelson, Heise, & Sidaway, 2001; McNeal & Sands, 2003; Young & Behm, 2003; Young & Elliott, 2001), and running speed (Nelson, Driscoll, Landin, Young, & Schexnayder, 2005; Siatras, Papadopoulos, Mameletzi, Gerodimos, Kellis, 2003). This paradox between accepted dogma and current research places a difficult decision on coaches and athletes. Do they include flexibility exercises in their preevent activities and risk the loss of maximal performance, or do they drop the flexibility exercises and increase the risk of injury? To help answer this question, it would be helpful to know if high flexibility has a different influence on force production. Unfortunately, little information is available about individuals’ degree of flexibility in the aforementioned studies. Four of the studies (Church et al., 2001; McNeal & Sands, 2003; Nelson et al., 2005; Siatras et al., 2003) made measurements on competitive athletes. While it is reasonable to assume that competitive athletes perform stretching exercises as part of their training regimen, one cannot be positive that these stretching exercises will routinely yield high flexibility. Moreover, two of the studies (McNeal & Sands, 2003; Siatras et al., 2003) used children whose mean ages were less than 13 years, thus, increasing rather than decreasing the number of possible confounding factors. In addition, the studies reporting the initial flexibility of the individuals tested (Kokkonen et al., 1998; Nelson & Kokkonen, 2001) reported sit-and-reach scores below the 50th percentile of the published norms (for norms, see Hoegar & Hoegar, 1990). Thus, it is possible that the negative impact of stretching is present primarily in individuals who do not regularly engage in stretching activities and/or whose sit-and-reach scores are below the recommended normal percentile (i.e., < 60th percentile for the sit-and-reach). Strength Inhibition Following An Acute Stretch Is Not Limited To Novice Stretchers

Early-Phase Resistance Training Strength Gains in Novice Lifters Are Enhanced by Doing Static Stretching

Kokkonen, J, Nelson, AG, Tarawhiti, T, Buckingham, P, and Winchester, JB. Early-phase resistance training strength gains in novice lifters are enhanced by doing static stretching. J Strength Cond Res 24(2): 502-506, 2010-This study investigated differences in lower-body strength improvements when using standard progressive resistance training (WT) vs. the same progressive resistance training combined with static stretching exercises (WT + ST). Thirty-two college students (16 women and 16 men) were pair matched according to sex and knee extension 1 repetition maximum (1RM). One person from each pair was randomly assigned to WT and the other to WT + ST. WT did 3 sets of 6 repetitions of knee extension, knee flexion, and leg press 3 days per week for 8 weeks with weekly increases in the weight lifted. The WT + ST group performed the same lifting program as the WT group along with static stretching exercises designed to stretch the hip, thigh, and calf muscle groups. Stretching exercise sessions were done twice a week for 30 minutes during the 8-week period. WT significantly (p < 0.05) improved their knee flexion, knee extension, and leg press 1RM by 12, 14, and 9%, respectively. WT + ST, on the other hand, significantly (p < 0.05) improved their knee flexion, knee extension, and leg press 1RM by 16, 27, and 31, respectively. In addition, the WT + ST group had significantly greater knee extension and leg press gains (p < 0.05) than the WT group. Based on results of this study, it is recommended that to maximize strength gains in the early phase of training, novice lifters should include static stretching exercises to their resistance training programs.

A 10-week stretching program increases strength in the contralateral muscle.

Nelson, AG, Kokkonen, J, Winchester, JB, Kalani, W, Peterson, K, Kenly, MS, and Arnall, DA. A 10-week stretching program increases strength in the contralateral muscle. J Strength Cond Res 26(3): 832–836, 2012—It was questioned whether a unilateral stretching program would induce a crosstraining effect in the contralateral muscle. To test this, 13 untrained individuals participated in a 10-week stretching program while 12 other untrained individuals served as a control group. For the experimental group, the right calf muscle was stretched 4 times for 30 seconds, with a 30-second rest between stretches, 3 d·wk−1 for 10 weeks. Strength, determined via 1 repetition maximum (1RM) unilateral standing toe raise, and range of motion (ROM) were measured pre-post. In the treatment group, the stretched calf muscle had a significant (p < 0.05) 8% increase in ROM, whereas the nonstretched calf muscle had a significant 1% decrease in ROM. The 1 RM of the stretched calf muscle significantly increased 29%, whereas the 1RM of the nonstretched calf muscle significantly increased 11%. In the control group, neither 1RM nor ROM changed for either leg. The results indicate that 10 weeks of stretching only the right calf will significantly increase the strength of both calves. Hence, chronic stretching can also induce a crosstraining effect for strength but not for the ROM. This study also validates earlier findings suggesting that stretching can elicit strength gains in untrained individuals.

Twenty minutes of passive stretching lowers glucose levels in an at-risk population: an experimental study

QUESTION Can passive static stretching lower blood glucose in an at-risk population? DESIGN Randomised, within-participant experimental study. PARTICIPANTS 22 adults (17 males) either at increased risk of Type 2 diabetes or with Type 2 diabetes. INTERVENTION The participants reported to the laboratory 2hr after eating a meal, and drank 355ml of fruit juice (∼43g carbohydrate). Thirty minutes later, they underwent either a 40min passive static stretching regimen or a mock passive stretching regimen. Stretching consisted of six lower body and four upper body static passive stretches. For the mock stretches, the same positions were adopted, but no tension was applied to the musculature. OUTCOME MEASURES Blood glucose levels for both the stretching and mock stretching were analysed from a finger prick sample using a hand-held glucometer. Values were obtained at baseline (0min), during the regimen (20min), and after the regimen (40min) on both study days. RESULTS Compared to mock stretch, stretching resulted in a significantly greater drop in blood glucose at 20min (mean difference 28mg/dL, 95% CI 13 to 43; or 1.57mmol/L, 95% CI 0.72 to 2.39). This effect was also statistically significant at 40min (mean difference 24mg/dL, 95% CI 9 to 39; or 1.35mmol/L, 95% CI 0.50 to 2.17). CONCLUSION These results suggest that passive static stretching of the skeletal muscles may be an alternative to exercise to help lower blood glucose levels.

Acute Stretching Increases Postural Stability in Nonbalance Trained Individuals

Abstract Nelson, AG, Kokkonen, J, Arnall, DA, and Li, L. Acute stretching increases postural stability in nonbalance trained individuals. J Strength Cond Res 26(11): 3095–3100, 2012—Studies into the relationship between acute stretching and maintenance of postural balance have been inconclusive. It was hypothesized that familiarization with the task and subsequent learning might be involved in the conflicting results. Therefore, this study was to designed determine if a regimen of static stretching exercises after a familiarization period would improve a persons ability to maintain a stabilometer in a neutral position and whether stretching had the same effect on individuals with extensive involvement with balancing tasks. Forty-two college students (21 male, 21 female) and 10 surfers (all male) performed tests on a stabilometer on 2 separate days after 3 days of familiarization. Testing followed either 30 minutes of quiet sitting (nonstretched) or 30 minutes of stretching activities (stretched). Stretching exercises consisted of various assisted and unassisted static stretches of the muscles around the hip, knee, and ankle joints. Improved flexibility after the stretching exercises was demonstrated by significant (p < 0.05) 6.5 ± 2.7 cm (mean ± SD) increase in the sit and reach. Balance time for the students improved significantly by 11.4% (2.0-second increase), but the surfers had no significant change. Thus, stretching improved maintenance of balance perhaps by helping the subjects to eliminate the gross muscle contractions that caused large stabilometer displacements and to replace them with fine muscle contractions that caused little or no stabilometer displacements. However, it appears that experience doing balance tasks supplants any stretching benefit.