Joke Kokkonen’s research while affiliated with Brigham Young University–Hawaii and other places

Background: Reductions in one repetition maximum lifts (1RM) following static stretching can be attributed to enhanced neural inhibition, which can be reduced by using stimulants like caffeine. This study compared knee-flexion 1RM following either static stretching (SS) or no-stretching (NS), as well as after ingesting either caffeine (C) or placebo (P). Methods: Twenty-four participants (12 female, 12 male) performed four random counterbalanced knee flexion 1RM tests. A 1RM test was performed for each condition at the same time of day with ~48 h separating each test. Static stretching consisted of 5 exercises with the 1RM being performed immediately following the stretching. Caffeine dose was 6 mg•kg-1 body weight, and the placebo was methylcellulose (520 mg). Both doses were administered as pills 60 min before the SS or NS procedures. Results: Two-way repeated measures ANOVA showed a significant main effect for [NS vs. SS] (p <0.001, ηG2 = 0.23). The main effect for [C vs. P], and the interaction between [C vs. P] and [NS vs. SS] were not statistically different. Average (± standard deviation) 1RM (N) were as follows: CNS = 512 ± 242, CSS = 474 ± 241, PNS = 498 ± 247, and PSS = 460 ± 247. Conclusions: It is concluded that static stretching induced strength decrements are not removed by using stimulants at doses allowed by sport governing organizations.

Muscle Sentry® is an exercise supplement that its manufacturer claims will give a person "gains in stamina and endurance, and increased cardiovascular efficiency" in both aerobic and anaerobic work. However, data concerning Muscle Sentry®’s influence on increased endurance and cardiovascular efficiency are only based on increases in VO2max. Actual changes in performance and cardiac work (i.e. heart VO2) have not been reported. Purpose: This study compared the total weight lifted and post-exercise estimated cardiac VO2 while on either Muscle Sentry® (MS) or placebo (PL). Method: Participants (11 women, 10 men, college students 20-24 years) performed 3 sets to failure of both chest and leg press using a load equal to their eight repetition maximum with 1 min rest separating each set. Each exercise was performed four times (2x MS, 2x PL) at the same time of day with 48 h separating each exercise. Both MS and PL were ingested 30 min prior to performing the exercise. Just prior to starting the exercise and immediately at the end of each set, both heart rate and blood pressure were obtained. The rate pressure product (RPP) was then calculated to determine estimated cardiac VO2. Daily RPP and total weight lifted (chest+leg) for each supplementation were averaged together, and each average final RPP was divided by the total weight lifted to obtain a normalized value. Results: Paired t-tests for total weight lifted (mean ± std. dev.: MS= 58334 ± 27213 N, PL= 59013 ± 28240 N) showed no significance between MS and PL. In addition, the adjusted RPP (MS= 0.308 ± 0.127, PL= 0.316 ± 0.135) was not significantly different. Conclusion: Ingestion of Muscle Sentry® 30 min prior to doing 3 sets to failure of both chest and leg presses had no effect upon either total work lifted or estimated cardiac VO2. This suggests that, in some instances, the benefits of Muscle Sentry® are less than those claimed by the manufacturer.

This study compared the number of bilateral leg presses done at 150% of body mass while on either Muscle Sentry® (MS) or placebo (PL). Participants (16 women, 14 men, college students 19–26 years) performed 2 sets of leg press to failure using 150% of their body mass with 5 min rest separating the 2 sets. Each exercise was performed twice (1× MS, 1× PL) at the same time of day with 48 h separating each exercise. Both MS and PL were ingested 30 min prior to performing the exercise. Just prior to starting the exercise and at the end of each set, heart rate, and blood pressure were obtained and the rate pressure product was calculated to determine myocardial workload. Two-way repeated measures ANOVA for lift number showed no significant main effects for either MS vs. PL, or for Set1 vs. Set2 (p > 0.05). The interaction was also not statistically different (mean repetitions ± std. dev.: MS1= 28±20, MS2= 26±18, PL1 = 30±24, PL2 = 29±20). Two-way repeated measures ANOVA for rate pressure product showed no significance for either the main effect for MS vs. PL, or supplement × pre-post interaction (p > 0.05). The main effect for pre-lift vs. post lift was significant (p<0.001) with post being higher than pre. Ingestion of Muscle Sentry® 30 min prior to leg pressing 150% of body mass to failure had no effect upon either total work performance or myocardial workload.

Background Since it has been shown that spending 18 h under dim light conditions can result in reduced handgrip endurance, it was questioned whether or not a shorter exposure to dim light (i.e., 1 h) would have similar influence upon muscular endurance. Therefore this study compared the number of weighted knee extension lifts that could be done after spending 1 h in either dim or bright light. Methods Participants (5 women, 11 men, college students 19-26 years) performed knee extension lifts to exhaustion with a load approximating 40% of their body weight. The lifts to exhaustion were measured immediately following 1 h of exposure to each of the following three conditions: dark (DL), room light (RL) and room light plus 5 mg melatonin (RLM). A minimum of 48 h separated each condition, and all participants started the exposures in a rested fed condition. Results Average (±SD) number of knee extension lifts for RL (62.0 ± 22.0) was significantly (p < 0.05) greater than DL (51.4 ± 14.7) and RLM (57.8 ± 22.9). The number of RLM knee extension lifts was not significantly different from DL. Exposure to 1 h of dim light immediately prior to activity can result in a reduction in thigh muscle endurance. The decline in performance to short-term dim light exposure was similar to that found following longer-term exposure. Conclusion It appears that light intensity can influence muscle endurance, however, at this time this effect cannot be directly related to endogenous melatonin production.

The purpose of this study was to determine the extent that a static stretching program could increase heart rate (HR) and oxygen consumption (VO2), and if the increases were sufficient to serve as a warm-up for aerobic activity.Methods The HR and VO2 of 15 male and 16 female college students were measured after either 12 min of passive static stretching (SS), or 12 min pseudo-stretching (PS), which consisted of moving through the stretching positions without placing the muscles on stretch. Four different lower body stretches were used with each stretch held for 30 s before the participant moved to a different position, with the circuit being repeated four times. VO2 was determined by averaging breath-by-breath measures over the total 12 min. HR was obtained every 30 s and the 24 values were averaged. Warm-up benefit was determined from the O2 deficit accrued during 7-min cycling at 60% VO2max.ResultsHR (beats/min, mean ± SD) for SS (84 ± 11) was a significant (p < 0.05) 9% greater than PS (78 ± 12). Similarly, VO2 (mL/min, mean ± SD) for SS (0.53 ± 0.13) was a significant 44% greater than PS (0.38 ± 0.11). The O2 deficit (L, mean ± SD) for SS (0.64 ± 1.54) was not different from PS (0.72 ± 1.61).Conclusion These data indicate that passive static stretching increases both HR and VO2, indicating that metabolic activity can be increased without muscle activation. The magnitude of the increases, however, is not sufficient to elicit a warm-up effect.

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.

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 person's 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.