David A. Arnall

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.

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.

Growth and overweight of Navajo youth: secular changes from 1955 to 1997.

OBJECTIVE: To examine the growth status, prevalence of risk of overweight and of overweight, and secular changes in growth status in Navajo youth from 1955 to 1997.SUBJECTS: 526 (256 males, 270 females) Navajo children 6–12 y of age.MEASUREMENTS: Stature and mass were measured and the body mass index (BMI) was calculated.ANALYSIS: All three variables were plotted relative to age- and sex-specific US reference data and the prevalence rates for risk of overweight and of overweight were estimated using the BMI as the criterion. The cut-off for the risk of overweight was the age- and sex-specific 85th and 95th percentiles of NHANES I, while the cut-off for overweight was a BMI≥95th percentiles. Age-specific sex differences were compared using independent samples t-tests. Secular changes for body size were estimated by comparing age- and sex-specific means for stature, mass, and the BMI in the present study and two previous studies in 1955 and 1989.RESULTS: No statistically significant differences were observed between sexes within age groups. In both sexes, mean age-specific stature appeared to be relatively stable around the 50th percentile of US reference values. Mean age-specific mass appeared to be relatively stable between the 50th and 90th percentiles of the reference values, while the mean BMI tended to fluctuate about the 85th percentile. Approximately 41% of the Navajo boys and girls 6–12 y of age had BMIs ≥85th percentiles of US reference data. Compared to corresponding data on Navajo youth in 1955 and 1989, the current sample was larger in mass and the BMI. The estimated rate of secular change in mass was about 1.5 kg/decade in younger boys and girls, and about 3 kg/decade in older boys and girls between 1955 and 1997. The estimated rate of secular change in the BMI was about 0.5–1.0 units/decade between 1955 and 1997, while that for stature was about 2 cm/decade between 1955 and 1997.CONCLUSIONS: The results are consistent with recent findings on the Navajo Health and Nutrition Survey that overweight is a serious public health concern across the lifespan in the Navajo, and that the problem begins in childhood. Furthermore, Navajo children appear to be heavier than about a decade ago.

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.

Effects of inspiratory muscle training and yoga breathing exercises on respiratory muscle function in institutionalized frail older adults: a randomized controlled trial.

Background:In older adults, respiratory function may be seriously compromised when a marked decrease of respiratory muscle (RM) strength coexists with comorbidity and activity limitation. Respiratory muscle training has been widely studied and recommended as a treatment option for people who are unable to participate in whole-body exercise training (WBET); however, the effects of inspiratory muscle training and yoga breathing exercises on RM function remain unknown, specifically in impaired older adults. Purpose:To evaluate the effects of inspiratory threshold training (ITT) and yoga respiratory training (YRT) on RM function in institutionalized frail older adults. Methods:Eighty-one residents (90% women; mean age, 85 years), who were unable to perform WBET (inability to independently walk more than 10 m), were randomly assigned to a control group or one of the 2 experimental groups (ITT or YRT). Experimental groups performed a supervised interval-based training protocol, either through threshold inspiratory muscle training device or yoga breathing exercises, which lasted 6 weeks (5 days per week). Outcome measures were collected at 4 time points (pretraining, intermediate, posttraining, and follow-up) and included the maximum respiratory pressures (maximum inspiratory pressure [MIP] and maximum expiratory pressure [MEP]) and the maximum voluntary ventilation (MVV). Results:Seventy-one residents completed the study: control (n = 24); ITT (n = 23); YRT (n = 24). The treatment on had a significant effect on MIP YRT (F6,204 = 6.755, P < .001, &eegr;2 = 0.166), MEP (F6,204 = 4.257, P < .001, &eegr;2 = 0.111), and MVV (F6,204 = 5.322, P < .001, &eegr;2 = 0.135). Analyses showed that the YRT group had a greater increase of RM strength (MIP and MEP) and endurance (MVV) than control and/or ITT groups. Conclusion:Yoga respiratory training appears to be an effective and well-tolerated exercise regimen in frail older adults and may therefore be a useful alternative to ITT or no training, to improve RM function in older population, when WBET is not possible.

The restorative effects of pulsed infrared light therapy on significant loss of peripheral protective sensation in patients with long-term type 1 and type 2 diabetes mellitus

Pulsed infrared light therapy (PILT) has been shown to increase peripheral sensation in diabetic patients with diabetic peripheral neuropathy (DPN). However, most studies last for very short periods, with the subjects receiving only 6–20 treatments. The purpose of this study was to evaluate the effectiveness of an eight-week course of PILT in reversing long-standing, profound DPN in patients with type 1 and type 2 diabetes. Twenty-two subjects with a diagnosis of type 1 (n=2) or type 2 (n=20) diabetes participated in the study. PILT was administered to one foot chosen at random with the other foot serving as a within-subject control (no treatment). Patients underwent 24 treatments (3 times/week, for eight weeks) for 30 min per treatment. Changes in peripheral protective sensation (PPS) were measured using Semmes-Weinstein monofilaments (SWM) ranging from 3.7 to 6.48. PILT improved PPS even in patients with long-standing chronic neuropathies whose initial pre-study sensation was not measurable with a 200-g SWM. PILT significantly improves PPS. While the exact mechanism of action is not understood, infrared light may improve peripheral neuropathies by improving foot perfusion by stimulating nitric oxide production.

Maximal respiratory pressure reference values for Navajo children ages 6–14

Since anthropometric variables are critical to the creation of pulmonary nomograms for FVC, FEV1, and other volumes and capacities, it is logical that anthropometric variables also influence the values of the maximal respiratory pressures (MRPs). Since nomograms are race‐specific, it is important that tribe‐specific tables of normal maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) be developed. To date normal tables for MRPs do not exist for Navajo children.

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.

Spirometry Reference Values for Navajo Children Ages 6-14 Years

Spirometry is the most important tool in diagnosing pulmonary disease and is the most frequently performed pulmonary function test. Since respiratory disease is the single greatest cause for morbidity and mortality on the Navajo Nation, the purpose of this study was to create new age and race‐specific pulmonary nomograms for Navajo children. Five hundred fifty‐eight healthy children, ages 6–14 years, attending Navajo Nation elementary schools in Arizona, were asked to perform spirometry to develop population‐specific and tribe‐specific nomograms for forced vital capacity (FVC), forced expiratory volume in 1 sec (FEV1), and FEV1 Ratio (FEV1/FVC). Spirometry tests from 284 girls and 274 boys met American Thoracic Society quality control standards. Lung function values, except for FEV1/FVC, all increased with height. The lower limit of the normal range for FEV1/FVC was 80%. The spirometry reference equations from the healthy boys and girls were developed. Height and the natural log of height were significant predictors of FEV1, FVC, and FEF25–75% in the gender‐specific models. The resulting population‐specific spirometry reference equations should be used when testing Navajo children ages 6–14 years. However, the use of the NHANES III spirometry reference equations for Caucasian children may not result in significant misclassification in clinical settings providing that a maximal effort is given by the Navajo child being tested. Pediatr Pulmonol. 2009; 44:489–496.