Showing papers in "Medicine and Science in Sports and Exercise in 2011"

Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory, Musculoskeletal, and Neuromotor Fitness in Apparently Healthy Adults: Guidance for Prescribing Exercise

Abstract: The purpose of this Position Stand is to provide guidance to professionals who counsel and prescribe individualized exercise to apparently healthy adults of all ages. These recommendations also may apply to adults with certain chronic diseases or disabilities, when appropriately evaluated and advised by a health professional. This document supersedes the 1998 American College of Sports Medicine (ACSM) Position Stand, "The Recommended Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory and Muscular Fitness, and Flexibility in Healthy Adults." The scientific evidence demonstrating the beneficial effects of exercise is indisputable, and the benefits of exercise far outweigh the risks in most adults. A program of regular exercise that includes cardiorespiratory, resistance, flexibility, and neuromotor exercise training beyond activities of daily living to improve and maintain physical fitness and health is essential for most adults. The ACSM recommends that most adults engage in moderate-intensity cardiorespiratory exercise training for ≥30 min·d on ≥5 d·wk for a total of ≥150 min·wk, vigorous-intensity cardiorespiratory exercise training for ≥20 min·d on ≥3 d·wk (≥75 min·wk), or a combination of moderate- and vigorous-intensity exercise to achieve a total energy expenditure of ≥500-1000 MET·min·wk. On 2-3 d·wk, adults should also perform resistance exercises for each of the major muscle groups, and neuromotor exercise involving balance, agility, and coordination. Crucial to maintaining joint range of movement, completing a series of flexibility exercises for each the major muscle-tendon groups (a total of 60 s per exercise) on ≥2 d·wk is recommended. The exercise program should be modified according to an individual's habitual physical activity, physical function, health status, exercise responses, and stated goals. Adults who are unable or unwilling to meet the exercise targets outlined here still can benefit from engaging in amounts of exercise less than recommended. In addition to exercising regularly, there are health benefits in concurrently reducing total time engaged in sedentary pursuits and also by interspersing frequent, short bouts of standing and physical activity between periods of sedentary activity, even in physically active adults. Behaviorally based exercise interventions, the use of behavior change strategies, supervision by an experienced fitness instructor, and exercise that is pleasant and enjoyable can improve adoption and adherence to prescribed exercise programs. Educating adults about and screening for signs and symptoms of CHD and gradual progression of exercise intensity and volume may reduce the risks of exercise. Consultations with a medical professional and diagnostic exercise testing for CHD are useful when clinically indicated but are not recommended for universal screening to enhance the safety of exercise.

2011 Compendium of Physical Activities: a second update of codes and MET values.

Abstract: Purpose:The Compendium of Physical Activities was developed to enhance the comparability of results across studies using self-report physical activity (PA) and is used to quantify the energy cost of a wide variety of PA. We provide the second update of the Compendium, called the 2011 Compend

Validation of accelerometer wear and nonwear time classification algorithm.

Abstract: Introduction: The use of movement monitors (accelerometers) for measuring physical activity (PA) in intervention and population-based studies is becoming a standard methodology for the objective measurement of sedentary and active behaviors and for the validation of subjective PA self-reports. A vital step in PA measurement is the classification of daily time into accelerometer wear and nonwear intervals using its recordings (counts) and an accelerometer-specific algorithm. Purpose: The purpose of this study was to validate and improve a commonly used algorithm for classifying accelerometer wear and nonwear time intervals using objective movement data obtained in the whole-room indirect calorimeter. Methods: We conducted a validation study of a wear or nonwear automatic algorithm using data obtained from 49 adults and 76 youth wearing accelerometers during a strictly monitored 24-h stay in a room calorimeter. The accelerometer wear and nonwear time classified by the algorithm was compared with actual wearing time. Potential improvements to the algorithm were examined using the minimum classification error as an optimization target. Results: The recommended elements in the new algorithm are as follows: 1) zero-count threshold during a nonwear time interval, 2) 90-min time window for consecutive zero or nonzero counts, and 3) allowance of 2-min interval of nonzero counts with the upstream or downstream 30-min consecutive zero-count window for detection of artifactual movements. Compared with the true wearing status, improvements to the algorithm decreased nonwear time misclassification during the waking and the 24-h periods (all P values < 0.001). Conclusions: The accelerometer wear or nonwear time algorithm improvements may lead to more accurate estimation of time spent in sedentary and active behaviors.

Comparison of Accelerometer Cut Points for Predicting Activity Intensity in Youth

Abstract: TROST, S. G., P. D. LOPRINZI, R. MOORE, and K. A. PFEIFFER. Comparison of Accelerometer Cut Points for Predicting Activity Intensity in Youth. Med. Sci. Sports Exerc., Vol. 43, No. 7, pp. 1360–1368, 2011. The absence of comparative validity studies has prevented researchers from reaching consensus regarding the application of intensity-related accelerometer cut points for children and adolescents. Purpose: This study aimed to evaluate the classification accuracy of five sets of independently developed ActiGraph cut points using energy expenditure, measured by indirect calorimetry, as a criterion reference standard. Methods: A total of 206 participants between the ages of 5 and 15 yr completed 12 standardized activity trials. Trials consisted of sedentary activities (lying down, writing, computer game), lifestyle activities (sweeping, laundry, throw and catch, aerobics, basketball), and ambulatory activities

Validation of wearable monitors for assessing sedentary behavior.

Abstract: Purpose: A primary barrier to elucidating the association between sedentary behavior (SB) and health outcomes is the lack of valid monitors to assess SB in a free-living environment. The purpose of this study was to examine the validity of commercially available monitors to assess SB. Methods: Twenty overweight (mean ± SD: body mass index = 33.7 ± 5.7 kg·m-2) inactive, office workers age 46.5 ± 10.7 yr were directly observed for two 6-h periods while wearing an activPAL (AP) and an ActiGraph GT3X (AG). During the second observation, participants were instructed to reduce sitting time. We assessed the validity of the commonly used cut point of 100 counts per minute (AG100) and several additional AG cut points for defining SB. We used direct observation (DO) using focal sampling with duration coding to record either sedentary (sitting/lying) or nonsedentary behavior. The accuracy and precision of the monitors and the sensitivity of the monitors to detect reductions in sitting time were assessed using mixed-model repeated-measures analyses. Results: On average, the AP and the AG100 underestimated sitting time by 2.8% and 4.9%, respectively. The correlation between the AP and DO was R2 = 0.94, and the AG100 and DO sedentary minutes was R2 = 0.39. Only the AP was able to detect reductions in sitting time. The AG 150-counts-per-minute threshold demonstrated the lowest bias (1.8%) of the AG cut points. Conclusions: The AP was more precise and more sensitive to reductions in sitting time than the AG, and thus, studies designed to assess SB should consider using the AP. When the AG monitor is used, 150 counts per minute may be the most appropriate cut point to define SB.

Velocity loss as an indicator of neuromuscular fatigue during resistance training.

Abstract: SANCHEZ-MEDINA, L., and J. J. GONZALEZ-BADILLO. Velocity Loss as an Indicator of Neuromuscular Fatigue during Resistance Training. Med. Sci. Sports Exerc., Vol. 43, No. 9, pp. 1725-1734, 2011. Purpose: This study aimed to analyze the acute mechanical and metabolic response to resistance exercise protocols (REP) differing in the number of repetitions (R) performed in each set (S) with respect to the maximum predicted number (P). Methods: Over 21 exercise sessions separated by 48-72 h, 18 strength-trained males (10 in bench press (BP) and 8 in squat (SQ)) performed 1) a progressive test for one-repetition maximum (1RM) and load-velocity profile determination, 2) tests of maximal number of repetitions to failure (12RM, 10RM, 8RM, 6RM, and 4RM), and 3) 15 REP (S R(P): 3 6(12), 3 8(12), 3 10(12), 3 12(12), 3 6(10), 3 8(10), 3 10(10), 3 4(8), 3 6(8), 3 8(8), 3 3(6), 3 4(6), 3 6(6), 3 2(4), 3 4(4)), with 5-min interset rests. Kinematic data were registered by a linear velocity transducer. Blood lactate and ammonia were measured before and after exercise. Results: Mean repetition velocity loss after three sets, loss of velocity pre-post exercise against the 1-mIs j1 load, and countermovement jump height loss (SQ group) were significant for all REP and were highly correlated to each other (r = 0.91-0.97). Velocity loss was significantly greater for BP compared with SQ and strongly correlated to peak postexercise lactate (r = 0.93-0.97) for both SQ and BP. Unlike lactate, ammonia showed a curvilinear response to loss of velocity, only increasing above resting levels when R was at least two repetitions higher than 50% of P. Conclusions: Velocity loss and metabolic stress clearly differs when manipulating the number of repetitions actually performed in each training set. The high correlations found between mechanical (velocity and coun- termovement jump height losses) and metabolic (lactate, ammonia) measures of fatigue support the validity of using velocity loss to

Validation of the GENEA Accelerometer.

Abstract: Purpose: The study aims were: 1) to assess the technical reliability and validity of the GENEA using a mechanical shaker; 2) to perform a GENEA value calibration to develop thresholds for sedentary and light-, moderate-, and vigorous-intensity physical activity; and 3) to compare the intensity classification of the GENEA with two widely used accelerometers. Methods: A total of 47 GENEA accelerometers were attached to a shaker and vertically accelerated, generating 15 conditions of varying acceleration and/or frequency. Reliability was calculated using SD and intrainstrument and interinstrument coefficients of variation, whereas validity was assessed using Pearson correlation with the shaker acceleration as the criterion. Next, 60 adults wore a GENEA on each wrist and on the waist (alongside an ActiGraph and RT3 accelerometer) while completing 10-12 activity tasks. A portable metabolic gas analyzer provided the criterion measure of physical activity. Analyses involved the use of Pearson correlations to establish criterion and concurrent validity and receiver operating characteristic curves to establish intensity cut points. Results: The GENEA demonstrated excellent technical reliability (CVintra = 1.4%, CVinter = 2.1%) and validity (r = 0.98, P < 0.001) using the mechanical shaker. The GENEA demonstrated excellent criterion validity using VO as the criterion (left wrist, r = 0.86; right wrist, r = 0.83; waist, r = 0.87), on par with the waist-worn ActiGraph and RT3. The GENEA demonstrated excellent concurrent validity compared with the ActiGraph (r = 0.92) and the RT3 (r = 0.97). The waist-worn GENEA had the greatest classification accuracy (area under the receiver operating characteristic curve (AUC) = 0.95), followed by the left (AUC = 0.93) and then the right wrist (AUC = 0.90). The accuracy of the waist-worn GENEA was virtually identical with that of the ActiGraph (AUC = 0.94) and RT3 (AUC = 0.95). CONCLUSION:: The GENEA is a reliable and valid measurement tool capable of classifying the intensity of physical activity in adults. © 2011 by the American College of Sports Medicine.

Influence of Resistance Exercise on Lean Body Mass in Aging Adults: A Meta-Analysis

Abstract: PETERSON, M. D., A. SEN, and P. M. GORDON. Influence of Resistance Exercise on Lean Body Mass in Aging Adults: A MetaAnalysis. Med. Sci. Sports Exerc., Vol. 43, No. 2, pp. 249–258, 2011. Purpose: Sarcopenia plays a principal role in the pathogenesis of frailty and functional impairment that occur with aging. There are few published accounts that examine the overall benefit of resistance exercise (RE) for lean body mass (LBM) while considering a continuum of dosage schemes and/or age ranges. Therefore, the purpose of this meta-analysis was to determine the effects of RE on LBM in older men and women while taking these factors into consideration. Methods: This study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses recommendations. Randomized controlled trials and randomized or nonrandomized studies among adults Q50 yr were included. Heterogeneity between studies was assessed using the Cochran Q and the I 2 statistics, and publication bias was evaluated through physical inspection of funnel plots as well as formal rank-correlation statistics. Mixed-effects meta-regression was incorporated to assess the relationship between RE dosage and changes in LBM. Results: Data from 49 studies, representing a total of 1328 participants, were pooled using random-effect models. Results demonstrated a positive effect for LBM, and there was no evidence of publication bias. The Cochran Q statistic for heterogeneity was 497.8, which was significant (P G 0.01). Likewise, I 2 was equal to 84%, representing rejection of the null hypothesis of homogeneity. The weighted pooled estimate of mean LBM change was 1.1 kg (95% confidence interval = 0.9–1.2 kg). Meta-regression revealed that higher-volume interventions were associated (A = 0.05, P G 0.01) with significantly greater increases in LBM, whereas older individuals experienced less increase (A = j0.03, P = 0.01). Conclusions: RE is effective for eliciting gains in LBM among aging adults, particularly with higher-volume programs. Findings suggest that RE participation earlier in life may provide superior effectiveness.

Effects of Step Rate Manipulation on Joint Mechanics during Running

Abstract: HEIDERSCHEIT, B. C., E. S. CHUMANOV, M. P. MICHALSKI, C. M. WILLE, and M. B. RYAN. Effects of Step Rate Manipulation on Joint Mechanics during Running. Med. Sci. Sports Exerc., Vol. 43, No. 2, pp. 296–302, 2011. Purpose: The objective of this study was to characterize the biomechanical effects of step rate modification during running on the hip, knee, and ankle joints so as to evaluate a potential strategy to reduce lower extremity loading and risk for injury. Methods: Three-dimensional kinematics and kinetics were recorded from 45 healthy recreational runners during treadmill running at constant speed under various step rate conditions (preferred, T5%, and T10%). We tested our primary hypothesis that a reduction in energy absorption by the lower extremity joints during the loading response would occur, primarily at the knee, when step rate was increased. Results: Less mechanical energy was absorbed at the knee (P G 0.01) during the +5% and +10% step rate conditions, whereas the hip (P G 0.01) absorbed less energy during the +10% condition only. All joints displayed substantially (P G 0.01) more energy absorption when preferred step rate was reduced by 10%. Step length (P G 0.01), center of mass vertical excursion (P G 0.01), braking impulse (P G 0.01), and peak knee flexion angle (P G 0.01) were observed to decrease with increasing step rate. When step rate was increased 10% above preferred, peak hip adduction angle (P G 0.01) and peak hip adduction (P G 0.01) and internal rotation (P G 0.01) moments were found to decrease. Conclusion :W e conclude that subtle increases in step rate can substantially reduce the loading to the hip and knee joints during running and may prove

Acute Dietary Nitrate Supplementation Improves Cycling Time Trial Performance

Abstract: Purpose:Dietary nitrate supplementation has been shown to reduce the O2 cost of submaximal exercise and to improve high-intensity exercise tolerance. However, it is presently unknown whether it may enhance performance during simulated competition. The present study investigated the effects o

Technical ability of force application as a determinant factor of sprint performance.

Abstract: Purpose:We transposed the concept of effectiveness of force application used in pedaling mechanics to calculate the ratio of forces (RF) during sprint running and tested the hypothesis that field sprint performance was related to the technical ability to produce high amounts of net positive

Low-volume interval training improves muscle oxidative capacity in sedentary adults.

Abstract: Introduction: High-intensity interval training (HIT) increases skeletal muscle oxidative capacity similar to traditional endurance training, despite a low total exercise volume. Much of this work has focused on young active individuals, and it is unclear whether the results are applicable to older less active populations. In addition, many studies have used "all-out" variable-load exercise interventions (e.g., repeated Wingate tests) that may not be practical for all individuals. We therefore examined the effect of a more practical low-volume submaximal constant-load HIT protocol on skeletal muscle oxidative capacity and insulin sensitivity in middle-aged adults, who may be at a higher risk for inactivity-related disorders. Methods: Seven sedentary but otherwise healthy individuals (three women) with a mean ± SD age, body mass index, and peak oxygen uptake (V?O2peak) of 45 ± 5 yr, 27 ± 5 kg·m-2, and 30 ± 3 mL·kg-1·min-1 performed six training sessions during 2 wk. Each session involved 10 × 1-min cycling at ~60% of peak power achieved during a ramp V?O2peak test (eliciting ~80%-95% of HR reserve) with 1 min of recovery between intervals. Needle biopsy samples (vastus lateralis) were obtained before training and ~72 h after the final training session. Results: Muscle oxidative capacity, as reflected by the protein content of citrate synthase and cytochrome c oxidase subunit IV, increased by ~35% after training. The transcriptional coactivator peroxisome proliferator-activated receptor ? coactivator 1a was increased by ~56% after training, but the transcriptional corepressor receptor-interacting protein 140 remained unchanged. Glucose transporter protein content increased ~260%, and insulin sensitivity, on the basis of the insulin sensitivity index homeostasis model assessment, improved by ~35% after training. Conclusions: Constant-load low-volume HIT may be a practical time-efficient strategy to induce metabolic adaptations that reduce the risk for inactivity-related disorders in previously sedentary middle-aged adults.

Disproportionate exercise load and remodeling of the athlete's right ventricle.

Abstract: PURPOSE: There is evolving evidence that intense exercise may place a disproportionate load on the right ventricle (RV) when compared with the left ventricle (LV) of the heart. Using a novel method of estimating end-systolic wall stress (ES-σ), we compared the RV and LV during exercise and assessed whether this influenced chronic ventricular remodeling in athletes. METHODS: For this study, 39 endurance athletes (EA) and 14 nonathletes (NA) underwent resting cardiac magnetic resonance (CMR), maximal oxygen uptake (VO2), and exercise echocardiography studies. LV and RV end-systolic wall stress (ES-σ) were calculated using the Laplace relation (ES-σ = Pr/(2h)). Ventricular size and wall thickness were determined by CMR; invasive and Doppler echo estimates were used to measure systemic and pulmonary ventricular pressures, respectively; and stroke volume was quantified by Doppler echocardiography and used to calculate changes in ventricular geometry during exercise. RESULTS: In EA, compared with NA, resting CMR measures showed greater RV than LV remodeling. The ratios RV ESV/LV ESV (1.40 ± 0.23 vs 1.26 ± 0.12, P = 0.007) and RV mass/LV mass (0.29 ± 0.04 vs 0.25 ± 0.03, P = 0.012) were greater in EA than in NA. RVES-σ was lower at rest than LVES-σ (143 ± 44 vs 252 ± 49 kdyn · cm, P < 0.001) but increased more with strenuous exercise (125% vs 14%, P < 0.001), resulting in similar peak exercise ES-σ (321 ± 106 vs 286 ± 77 kdyn · cm, P = 0.058). Peak exercise RVES-σ was greater in EA than in NA (340 ± 107 vs 266 ± 82 kdyn · cm, P = 0.028), whereas RVES-σ at matched absolute workloads did not differ (P = 0.79). CONCLUSIONS: Exercise induces a relative increase in RVES-σ which exceeds LVES-σ. In athletes, greater RV enlargement and greater wall thickening may be a product of this disproportionate load excess.

Exercise Autonomous Motivation Predicts 3-yr Weight Loss in Women

Abstract: SILVA, M. N., D. MARKLAND, E. V. CARRACA, P. N. VIEIRA, S. R. COUTINHO, C. S. MINDERICO, M. G. MATOS, L. B. SARDINHA, and P. J. TEIXEIRA. Exercise Autonomous Motivation Predicts 3-yr Weight Loss in Women. Med. Sci. Sports Exerc., Vol. 43, No. 4, pp. 728–737, 2011. Purpose: This study evaluated exercise-related predictors of successful long-term weight control in women by analyzing the extent to which sustained exercise participation and self-determination theory (SDT)–based exercise motivation variables mediated the impact of a behavioral weight control intervention on 3-yr weight change. Methods: Longitudinal randomized controlled trial consisting of a 1-yr SDT-based intervention and a 2-yr follow-up with 221 female participants (means T SD: age = 37.6 T 7 yr, body mass index = 31.6 T 4.1 kgIm j2 ). The tested model incorporated experimentally manipulated perceived need support, motivational regulations, and 2-yr exercise adherence as mediators of the intervention’s impact on 3-yr weight change. Paths were tested using partial least squares analysis. Where there were significant intervening paths, tests of mediation were conducted. Results: Treatment had significant effects on 1- and 2-yr autonomous regulations, 2-yr physical activity, and 3-yr weight change, fully mediated by the tested paths (effect ratio = 0.10–0.61). Moderate and vigorous exercise at 2 yr had a significant effect (P G 0.001) on weight loss success at 3 yr and partially mediated the effect of treatment on weight change. The 2-yr autonomous regulation effects on follow-up weight change were only partially mediated by physical activity (effect ratio = 0.42). Conclusions: This application of SDT to physical activity and weight management showed that not all types of motivation predict long-term behavioral outcomes and that sustained moderate and vigorous exercise mediated long-term weight change. It provides strong evidence for a link between experimentally increased autonomous motivation and exercise and long-term weight loss maintenance. Results highlight the importance of interventions targeting the

Slow component of VO2 kinetics: mechanistic bases and practical applications.

Abstract: The V·O₂ slow component, a slowly developing increase in V·O₂ during constant-work-rate exercise performed above the lactate threshold, represents a progressive loss of skeletal muscle contractile efficiency and is associated with the fatigue process. This brief review outlines the current state of knowledge concerning the mechanistic bases of the V·O₂ slow component and describes practical interventions that can attenuate the slow component and thus enhance exercise tolerance. There is strong evidence that, during constant-work-rate exercise, the development of the V·O₂ slow component is associated with the progressive recruitment of additional (type II) muscle fibers that are presumed to have lower efficiency. Recent studies, however, indicate that muscle efficiency is also lowered (resulting in a "mirror-image" V·O₂ slow component) during fatiguing, high-intensity exercise in which additional fiber recruitment is unlikely or impossible. Therefore, it seems that muscle fatigue underpins the V·O₂ slow component, although the greater fatigue sensitivity of recruited type II fibers might still play a crucial role in the loss of muscle efficiency in both situations. Several interventions can reduce the magnitude of the V·O₂ slow component, and these are typically associated with an enhanced exercise tolerance. These include endurance training, inspiratory muscle training, priming exercise, dietary nitrate supplementation, and the inspiration of hyperoxic gas. All of these interventions reduce muscle fatigue development either by improving muscle oxidative capacity and thus metabolic stability or by enhancing bulk muscle O2 delivery or local Q·O₂-to-V·O₂ matching. Future honing of these interventions to maximize their impact on the V·O₂ slow component might improve sports performance in athletes and exercise tolerance in the elderly or in patient populations.

Functional movement screening: predicting injuries in officer candidates.

Abstract: PURPOSE:: Functional movement screening (FMS) is a musculoskeletal assessment method that incorporates seven movements and yields an overall score based on movement quality. The objective of this study was to document the distribution of scores and determine if FMS scores could predict injury in a large military cohort. METHODS:: A cohort of 874 Marine officer candidates were recruited, consented, completed demographic questionnaires, and had FMS performed during medical in-processing. Candidates were enrolled in either long cycle (LC: 68 days; n=427) or short cycle (SC: 38 days; n=447) training and followed for injuries occurring in training. RESULTS:: The mean FMS score (score range=0-21) among all candidates was 16.6 ± 1.7; approximately 10% of candidates had FMS scores ≤ 14. A score of ≤14 on the FMS predicted any injury with a sensitivity of 0.45 and a specificity of 0.71 and serious injury with a sensitivity of 0.12 and a specificity of 0.94. Both LC and SC cohorts demonstrated higher injury risk among candidates who had scores ≤14 compared to those with scores >14 (LC: risk ratio (RR)=1.65 (95% CI=1.05 -2.59 p= 0.03); SC: RR=1.91 (95% CI=1.21-3.01 p Language: en

Effect of Running Speed on Lower Limb Joint Kinetics

Abstract: SCHACHE, A. G., P. D. BLANCH, T. W. DORN, N. A. T. BROWN, D. ROSEMOND, and M. G. PANDY. Effect of Running Speed on Lower Limb Joint Kinetics. Med. Sci. Sports Exerc., Vol. 43, No. 7, pp. 1260–1271, 2011. Purpose: Knowledge regarding the biomechanical function of the lower limb muscle groups across a range of running speeds is important in improving the existing understanding of human high performance as well as in aiding in the identification of factors that might be related to injury. The purpose of this study was to evaluate the effect of running speed on lower limb joint kinetics. Methods: Kinematic and ground reaction force data were collected from eight participants (five males and three females) during steady-state running on an indoor synthetic track at four discrete speeds: 3.50 T 0.04, 5.02 T 0.10, 6.97 T 0.09, and 8.95 T 0.70 mIs j1 . A standard inverse-dynamics approach was used to compute three-dimensional torques at the hip, knee, and ankle joints, from which net powers and work were also calculated. A total of 33 torque, power, and work variables were extracted from the data set, and their magnitudes were statistically analyzed for significant speed effects. Results: The torques developed about the lower limb joints during running displayed identifiable profiles in all three anatomical planes. The sagittal-plane torques, net powers, and work done at the hip and knee during terminal swing demonstrated the largest increases in absolute magnitude with faster running. In contrast, the work done at the knee joint during stance was unaffected by increasing running speed, whereas the work done at the ankle joint during stance increased when running speed changed from 3.50 to 5.02 mIs j1 , but it

Run Sprint Interval Training Improves Aerobic Performance but Not Maximal Cardiac Output

Abstract: Repeated maximal-intensity short-duration exercise (sprint interval training, SIT) can produce muscle adaptations similar to endurance training (ET) despite a much reduced training volume. However, most SIT data use cycling, and little is known about its effects on body composition or maximal cardiac output (Q?max). Purpose: The purpose of this study was to assess body composition, 2000-m run time trial, V?O2max, and Q?max effects of run SIT versus ET. Methods: Men and women (n = 10 per group; mean ± SD: age = 24 ± 3 yr) trained three times per week for 6 wk with SIT, 30-s all-out run sprints (manually driven treadmill), four to six bouts per session, 4-min recovery per bout, versus ET, 65% V?O2max for 30 to 60 min·d-1. Results: Training improved (P < 0.05) body composition, 2000-m run time trial performance, and V?O2max in both groups. Fat mass decreased 12.4% with SIT (mean ± SEM; 13.7 ± 1.6 to 12.0 ± 1.6 kg) and 5.8% with ET (13.9 ± 1.7 to 13.1 ± 1.6 kg). Lean mass increased 1% in both groups. Time trial performance improved 4.6% with SIT (-25.6 ± 8.1 s) and 5.9% with ET (-31.9 ± 6.3 s). V?O2max increased 11.5% with SIT (46.8 ± 1.6 to 52.2 ± 2.0 mL·kg·-1·min-1) and 12.5% with ET (44.0 ± 2.0 to 49.5 ± 2.6 mL·kg-1·min-1). None of these improvements differed between groups. In contrast, Q?max increased by 9.5% with ET only (22.2 ± 2.0 to 24.3 ± 1.6 L·min-1). Conclusions: Despite a fraction of the time commitment, run SIT induces similar body composition, V?O2max, and performance adaptations as ET, but with no effect on Q?max. These data suggest that adaptations with ET are of central origin primarily, whereas those with SIT are more peripheral

Peak Oxygen Uptake and Cardiovascular Risk Factors in 4631 Healthy Women and Men

Abstract: Introduction: Many studies suggest that cardiorespiratory fitness, measured as peak oxygen uptake (V?O2peak), may be the single best predictor of cardiovascular morbidity and premature cardiovascular mortality. However, current reference values are either estimates of oxygen uptake or come from small studies, mainly of men. Therefore, the aims of this study were to directly measure V?O2peak in healthy adult men and women and to assess the association with cardiovascular risk factor levels. Methods: A cross-sectional study of 4631 volunteering, free-living Norwegian men (n = 2368) and women (n = 2263) age 20-90 yr. The data collection was from June 2007 to June 2008. Participants were free from known pulmonary or cardiovascular disease. V?O2peak was measured by ergospirometry during treadmill running. Associations (odds ratios, OR) with unfavorable levels of cardiovascular risk factors and a cluster of cardiovascular risk factors were assessed by logistic regression analysis. Results: Overall, mean V?O2peak was 40.0 ± 9.5 mL·kg-1·min-1. Women below the median V?O2peak (<35.1 mL·kg-1·min-1) were five times (OR = 5.4, 95% confidence interval = 2.3-12.9) and men below the median (<44.2 mL·kg-1·min-1) were eight times (OR = 7.9, 95% confidence interval = 3.5-18.0) more likely to have a cluster of cardiovascular risk factors compared to those in the highest quartile of V?O2peak (=40.8 and =50.5 mL·kg-1·min-1 in women and men, respectively). Each 5-mL·kg-1·min-1 lower V?O2peak corresponded to ~56% higher odds of cardiovascular risk factor clustering. Conclusions: These data represent the largest reference material of objectively measured V?O2peak in healthy men and women age 20-90 yr. Even in people considered to be fit, V?O2peak was clearly associated with levels of conventional cardiovascular risk factors.

Hamstring Musculotendon Dynamics during Stance and Swing Phases of High Speed Running

Abstract: Introduction—Hamstring strain injuries are common in sports that involve high speed running. It remains uncertain whether the hamstrings are susceptible to injury during late swing phase, when the hamstrings are active and lengthening, or during stance, when contact loads are present. In this study we used forward dynamic simulations to compare hamstring musculotendon stretch, loading and work done during stance and swing phases of high speed running gait cycles. Methods—Whole body kinematics, EMG activities and ground reactions were collected as 12 subjects ran on an instrumented treadmill at speeds ranging from 80% to maximum (average of 7.8 m/s). Subject-specific simulations were then created using a whole body musculoskeletal model that included fifty-two Hill-type musculotendon units acting about the hip and knee. A computed muscle control algorithm was used to determine muscle excitation patterns that drove the limb to track measured hip and knee sagittal plane kinematics, with measured ground reactions applied to the limb. Results—The hamstrings lengthened under load from 50% to 90% of the gait cycle (swing), and then shortened under load from late swing through stance. While peak hamstring stretch was invariant with speed, lateral hamstring (biceps femoris) loading increased significantly with speed, and was greatest during swing at the fastest speed. The biarticular hamstrings performed negative work on the system only during swing phase, with the amount of negative work increasing significantly with speed. Conclusion—We concluded that the large inertial loads during high speed running appear to make the hamstrings most susceptible to injury during swing phase when compared to stance phase. This information is relevant for scientifically establishing effective muscle injury prevention and rehabilitation programs.

Comparative validity of physical activity measures in older adults.

Abstract: Purpose: To compare the validity of various physical activity measures with doubly labeled water (DLW)-measured physical activity energy expenditure (PAEE) in free-living older adults. Methods: Fifty-six adults aged =65 yr wore three activity monitors (New Lifestyles pedometer, ActiGraph accelerometer, and a SenseWear (SW) armband) during a 10-d free-living period and completed three different surveys (Yale Physical Activity Survey (YPAS), Community Health Activities Model Program for Seniors (CHAMPS), and a modified Physical Activity Scale for the Elderly (modPASE)). Total energy expenditure was measured using DLW, resting metabolic rate was measured with indirect calorimetry, the thermic effect of food was estimated, and from these, estimates of PAEE were calculated. The degree of linear association between the various measures and PAEE was assessed, as were differences in group PAEE, when estimable by a given measure. Results: All three monitors were significantly correlated with PAEE (r = 0.48-0.60, P < 0.001). Of the questionnaires, only CHAMPS was significantly correlated with PAEE (r = 0.28, P = 0.04). Statistical comparison of the correlations suggested that the monitors were superior to YPAS and modPASE. Mean squared errors for all correlations were high, and the median PAEE from the different tools was significantly different from DLW for all but the YPAS and regression-estimated PAEE from the ActiGraph. Conclusions: Objective devices more appropriately rank PAEE than self-reported instruments in older adults, but absolute estimates of PAEE are not accurate. Given the cost differential and ease of use, pedometers seem most useful in this population when ranking by physical activity level is adequate.

Central and peripheral fatigue: interaction during cycling exercise in humans.

Abstract: Existing evidence suggests that exercise-induced alterations of the metabolic milieu of locomotor muscle and associated peripheral muscle fatigue affect the central projection of thin-fiber muscle afferents. These neurons provide inhibitory feedback to the CNS and thereby influence the magnitude of central motor drive during high-intensity whole-body endurance exercise. The purpose of this proposed feedback loop would be to regulate and restrict the development of exercise-induced peripheral muscle fatigue and/or associated sensory feedback to an "individual critical threshold." This centrally mediated restriction in the development of peripheral locomotor muscle fatigue might thereby help to prevent excessive disturbance of muscle homeostasis and potential harm to the organism. It seems that the regulatory mechanism is dominant during exercise under "normal" conditions but might become secondary in the face of extreme environmental influences such as severe hypoxia or heat. Most recent data are used to emphasize how the proposed feedback loop might be a key factor limiting performance during high-intensity whole-body endurance exercise.

Valgus plus internal rotation moments increase anterior cruciate ligament strain more than either alone.

Abstract: Purpose: To test the influence of combined knee valgus and internal tibial rotation moment on anterior cruciate ligament (ACL) strain during single-leg landing. We tested the following hypotheses: the combination of the valgus and internal rotation moments observed during single-leg landing produces a higher ACL strain than either moment applied individually, the combined rotational moments at the physiological levels observed could theoretically increase strain in the ACL high enough to rupture the ACL, and the location of the peak contact force was at the posterior-lateral side for combined loading. Methods: The study was conducted by applying in vivo human loading data to a validated simulation model of the three-dimensional dynamic knee joint to predict ACL strains. Results: The peak ACL strain increased nonlinearly when either applied valgus moment or internal rotation moment was increased in the model. When the two rotational moments were applied individually, neither caused ACL strain >0.077. However, when applied in combination, the two rotational moments had a much larger effect, and the predicted peak ACL strain increased up to 0.105. During landing, the peak contact force occurred at the posterior-lateral side of the tibial cartilage in the model when the combined maximum valgus moment and tibial internal rotation moments were applied. Conclusions: Combined knee valgus and internal rotation moments increases ACL strain more than either alone. The combination of a valgus and internal rotational moment at magnitudes that occurs in vivo during landing can cause ACL strains that may be high enough to cause ACL rupture. This predicted high ACL strain and the contact force location suggest that combined valgus and internal tibial rotational moments during single-leg landing are relevant to ACL injuries.

Objectively measured physical activity in a diverse sample of older urban UK adults

Abstract: Background:There are many health and social benefits of physical activity (PA) for older adults, but little is known about their activity patterns.Purpose:The purpose of this study was to objectively assess the PA patterns of older adults and the lifestyle and demographic factors associated

Match-Related Fatigue in Soccer Players

Abstract: Soccer induces neuromuscular fatigue requiring several hours of recovery. Purpose: The study aimed to determine the extent to which neuromuscular fatigue occurs in high-level professional players and its recovery after a match and to examine its relationship with central and peripheral fatigue indicators. Methods: Maximal voluntary contraction (MVC), sprint and passing abilities, muscle soreness, maximal voluntary activation, EMG activity, and evocated quadriceps contractile properties (using different electrical stimulations) were determined before, immediately after, and at 24 and 48 h after the match in 20 male professional players. Results: Immediately after a 90-min game, fatigue was evident by a reduction of MVC and sprint performance (-11%, P < 0.001 and -3%, P < 0.001, respectively) and increased muscle soreness (P < 0.001) compared with baseline, whereas short-passing ability was preserved. At the same time point, maximal voluntary activation and EMG activity were reduced by 8% (P < 0.001) and 12% (P = 0.001), respectively. M-wave characteristics were unchanged, whereas quadriceps mechanical responses to single and paired stimulations at 10 Hz resulted as significantly reduced (peak torque = -8%, P < 0.001 and -9%, P < 0.001). Despite the observation of a partial recovery 24 h after the game, all variables did not return to baseline values until 48 h after the match. Conclusions: In high-level professional players, the fatigue induced by a soccer match occurs to a smaller extent than in lower level athletes and seems to be recovered in a faster fashion. Match-related fatigue is determined by a combination of central and peripheral factors. A relationship exists between central fatigue indicators and MVC and sprint performance decrements, whereas muscle soreness seems to be linked to peripheral fatigue indicators, particularly to mechanical responses at low-frequency stimulations

A Reverse Pathway? Actual and Perceived Skill Proficiency and Physical Activity

Abstract: Purpose: Motor skills are considered a prerequisite to physical activity, yet the relationship may be reciprocal and perceived sports competence might mediate associations. Methods: In 2006/2007, 215 adolescents completed motor skill proficiency (Get Skilled Get Active), perceived sport competence (Physical Self-Perception Profile) and physical activity assessments (Adolescent Physical Activity Recall Questionnaire) as part of the Physical Activity and Skills Study. Using AMOS (Version 7.0), reciprocal relationships were examined between motor skill (object control and locomotor) and moderate to vigorous physical activity (MVPA). Both models were then run in different versions to understand the role of perceived sports competence as a potential mediator. Results: Mean age was 16.4 yr (SD = 0.6), 51.6% (111/215) were females. A reciprocal relationship between object control and MVPA and a one-way relationship from MVPA to locomotor skill was found. When perceived sports competence was examined as a mediator, the best-fitting model versions explained 16% (R² = 0.16) MVPA variation, and 30% object control (R² = 0.30), and 12% locomotor skill variation (R² = 0.12) (reverse relationship). Perceived sports competence partially mediates the relationship between object control proficiency and physical activity for both directions and fully mediates the relationship between physical activity and locomotor skill; but only when locomotor skill is the outcome. Conclusions: If the relationship between object control skill and physical activity is viewed as a ‘‘positive feedback loop,’’ skill development and increasing physical activity should simultaneously be targeted in physical activity interventions. Increasing perceived sport competence should also be an intervention focus.

72-h kinetics of high-sensitive troponin T and inflammatory markers after marathon.

Abstract: Introduction: Strenuous exercise induces significant increases in cardiac biomarkers. However, it is still unclear whether this is caused by cardiomyocyte necrosis or secondary mechanisms such as ischemia, cardiac energy deficiency, increased inflammation, or renal dysfunction. Methods: Therefore, we investigated cardiac biomarkers (high-sensitive cardiac troponin T (hs-cTnT), N-terminal pro-brain natriuretic peptide (NT-proBNP), heart-type fatty acid-binding protein (h-FABP)), inflammation markers (high-sensitive C-reactive protein (hs-CRP), interleukin-6 (IL-6), interleukin-10, tumor necrosis factor-a), and renal function (cystatin C) in 102 healthy men age 42 ± 9 yr before and 0, 24, and 72 h after a marathon. Results: Kinetics of hs-cTnT revealed a peak immediately after the race (V3) that decreased rapidly to pretest values within 72 h (V5) (median (interquartile range) = 31.07 (19.25-46.86) ng·L-1 at V3 and 3.61 (3.20-6.70) ng·L-1 at V5, P < 0.001). NT-proBNP and h-FABP kinetics showed a similar pattern (NT-proBNP = 92.6 (56.9-149.7) ng·L-1 at V3 and 34.9 (21.7-54.5) ng·L-1 at V5; h-FABP = 44.99 (32.19-64.42) µg·L-1 at V3 and 7.66 (5.64-10.60) µg·L-1 at V5; always P < 0.001). Proinflammatory markers, such as IL-6 and hs-CRP, and renal dysfunction were significantly augmented immediately after the race (before the race compared with maximum after the race: IL-6 = 15.5-fold, hs-CRP = 28-fold, cystatin C = 1.22-fold, all P < 0.001). These increases were not related to the increase of hs-cTnT. Similarly, training history, finishing time, and exercise intensity were not associated with changes of hs-cTnT. Conclusions: Cardiac biomarkers were increased immediately after a marathon race. Interestingly, values returned to normal levels within 72 h. These kinetics with a sharp peak indicate that cardiac necrosis during marathon running seems very unlikely but may be explained by altered myocyte metabolism

Vitamin D status relative to diet, lifestyle, injury, and illness in college athletes.

Abstract: Vitamin D deficiency is endemic in the general population; however, there is much to be learned about the vitamin D status of athletes. Purpose: The purposes of this study were to assess the prevalence of vitamin D insufficiency in collegiate athletes and to determine whether 25(OH)D concentrations are related to vitamin D intake, sun exposure, body composition, and risk for illness or athletic injury. Methods: 25(OH) vitamin D concentrations were measured in 41 athletes (18 men/23 women, 12 indoor/29 outdoor athletes) throughout the academic year. Dietary intake and lifestyle habits were assessed via questionnaire, bone density was measured by dual energy x-ray absorptiometry, and injury and illness were documented as part of routine care. Results: The 25(OH)D concentrations changed across time (P = 0.001) and averaged 49.0 ± 16.6, 30.5 ± 9.4, and 41.9 ± 14.6 ng·mL-1 (mean ± SD) in the fall, winter, and spring, respectively, and were higher in outdoor versus indoor athletes in the fall (P < 0.05). Using 40 ng·mL-1 as the cutoff for optimal status, 75.6%, 15.2%, and 36.0% of athletes had optimal status in the fall, winter, and spring, respectively. 25(OH)D concentrations were significantly (P < 0.05) correlated with multivitamin intake in the winter (r = 0.39) and tanning bed use in the spring (r = 0.48); however, status was otherwise not related to intake, lifestyle factors, or body composition. 25(OH)D concentrations in the spring (r = -0.40, P = 0.048) was correlated with frequency of illness. Conclusions: Our results suggest that collegiate athletes can maintain sufficient status during the fall and spring but would benefit from supplementation during the winter to prevent seasonal decreases in 25(OH)D concentrations. Results further suggest that insufficient vitamin D status may increase risk for frequent illness. Future research is needed to identify whether vitamin D status influences injury risk during athletic training or competition