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Precise quantification of physical activity is necessary in order to evaluate the relationship between physical activity and various types of disease and/or risk factors associated with disease. With the emergence of the study of the origins of coronary heart disease risk factors in children, it is imperative that accurate measurement of physical activity in the pediatric population be obtained. This review critically evaluates various field measures of physical activity in children including motion sensors, questionnaires, and heart rate. A new heart-rate quantification procedure is also presented that may provide an index of the quality of physical activity.

In this study, running economy differences between boys and men at a common speed (ABS = 9.6 kph) and at a relative speed adjusted for body size (REL = 3.71 leg lengths per second) were examined. The caloric cost relative to mass was significantly higher for the boys for ABS (men = .17, boys = .20), but not for REL (both .19). The relative heart rate (%HRmax) and ventilatory equivalent were higher for the boys at ABS, but not at REL. Boys had significantly higher stride frequencies in both conditions. Stride length/leg length was greater for boys during ABS, and for men during REL. Respiratory exchange ratios (RERs) were not different at ABS (men = .94, boys = .96), but during REL, boys had a significantly lower RER (.93 vs. .98). Running economy differences between adults and children are reduced when speeds are adjusted relative to body size. This model may be useful for identifying developmentally based differences in the physiology and biomechanics associated with exercise.

This review summarizes the research relating physical activity to aerobic fitness among adolescents. A brief description of commonly used physical activity and aerobic fitness measures is presented, followed by an interpretation of the literature that suggests a small to moderate relationship between physical activity and aerobic fitness in this population (typical correlation of .16-17). Dose-response data are lacking, which makes it difficult to offer definitive conclusions concerning the amount of physical activity necessary to elicit change in aerobic capacity. Nevertheless, recommendations about the type, amount, and quality of physical activity for adolescents are presented. Recommendations are based on a summary of the research data on daily physical activity and aerobic fitness in adolescents. Further research is needed to investigate the association between habitual physical activity and aerobic fitness in adolescents where the a priori goal is to identify a threshold of daily physical activity necessary for an aerobic benefit associated with enhanced health.

This study involved an 8-day protocol to determine the effects of delayed-onset muscle soreness (DOMS) on the mechanics of the lower extremity and on oxygen consumption during level running. On Day 1 the subjects, 10 healthy female recreational runners, were administered a treadmill max V̇O₂ test. They completed a 30-min downhill run on Day 3 to induce muscle soreness. On Days 2, 5, and 8 they completed a 15-min level run at a speed corresponding to 80% of V̇O₂max. Subsequent to each run the subjects completed a muscle soreness questionnaire and a blood sample was taken for creatine kinase (CK) analysis. Data analysis revealed statistically significant between-day differences for perceived muscle soreness and CK activity. However, metabolic cost was not different between days. There were significant differences between days in maximum ankle support dorsiflexion and plantar flexion and maximum knee flexion during both support and swing. None of the global parameters describing the total stride produced significant differences between Days 2 and 5. Therefore DOMS appeared to have little effect on V̇O₂ and a small effect on the kinematics of the lower extremity.

The sport of wrestling often encourages participants to engage in extreme weight loss practices in order to compete in a weight class one to three weight categories below normal weight. This review discusses the prevalence of the problem, methods wrestlers use to accomplish weight loss, and the health and performance consequences of rapid weight loss, with particular emphasis on weight cycling and minimal safe wrestling weight assessment. Some useful and practical recommendations for minimizing extreme weight loss practices are presented. Several state wrestling associations have adjusted their rules and regulations based on recommendations by organizations such as the American College of Sports Medicine to reduce the prevalence of the problem. Nevertheless, extreme weight loss continues to be a concern among health professionals, particularly with regard to health and performance.

In recent years, there has been tremendous growth in the use of wearable activity trackers in biomedical research. Activity trackers are also becoming more popular with consumers, who are able to share their data with researchers and practitioners. Steps per day is a useful variable that is estimated from most wearable activity trackers. It has intuitive meaning, is strongly associated with health variables, and has the potential to be standardized across devices. Activity trackers and other wearable medical devices could provide new information on health-related behaviors and their interaction with genetic and environmental variables. If integrated into medical practice, wearable technologies could help motivate patients to change their health behaviors and might eventually be used to diagnose medical conditions. The convergence of wearable medical devices, computer applications, smart phones, and electronic medical records could influence the practice of lifestyle medicine.

The effects of dietary supplementation with Coenzyme Q10 (CoQlO), a reputed performance enhancer and antioxidant, on physiological and biochemical parameters were examined. Ten male bicycle racers performed graded cycle ergometry both before and after being given 100 mg per day CoQlO or placebo for 8 weeks. Analysis of variance showed a significant difference between groups for postsupplementation serum CoQ10. Although both groups demonstrated training related improvements in all physiological parameters over the course of the study, there were no significant differences between the two groups (p>.05). Both groups showed a 21 % increase in serum MDA (an index of lipid peroxidation) after the presupplementation exercise test. After 8 weeks this increase was only 5 % , and again was identical for both groups. Supplementation with CoQlO has no measurable effect on cycling performance, ${\text{VO}}_2\max$ , submaximal physiological parameters, or lipid peroxidation. However, chronic intense training seems to result in marked attenuation of exercise-induced lipid peroxidation.

We evaluated the accuracy and precision of wearable activity trackers and a pedometer (ATPs) in estimating steps and sedentary time (ST) in free-living settings. Thirty-two healthy men and women (M ± SD: age = 32.3 ± 13.3 years; BMI = 24.4 ± 3.3 kg·m⁻²) were directly observed during three, 2-hour sessions on different days while wearing 10 devices and a biometric shirt. A validated direct observation (DO) system provided criterion measures for steps and ST. For steps, bias ranged from −753 steps/2-hrs (Fitbit Flex) to −57 steps/2-hrs (Polar Loop) and CIs ranged from [−1,144, −365] (Fitbit Flex) to [−291,175] (Polar Loop) steps/2-hrs. For all devices, step estimates were strongly correlated (r = 0.90 [Fitbit Flex] to r = 0.97 [New Lifestyles pedometer model 1000]) with DO counted steps. Estimates of ST were not accurate and were weakly correlated (r = −0.06 and r = 0.06 for Fitbit Flex and Fitbit One, respectively) with DO ST. Most ATPs were not accurate and varied in precision in estimating steps and ST in free-living settings. Implications from this study are that although point estimates of steps from ATPs are not accurate, ATPs’ ranking of step counts among individuals was high. However, the Fitbit Flex and Fitbit One are not recommended for estimating ST. This study advances our understanding of the performance of ATPs in estimating steps and ST in free-living settings, and significantly advances activity tracker and pedometer validation studies.

The relationship between physical activity measured using the LSI (Large Scale Integrated Activity Monitor), and questionnaire, with physical work capacity 170 (PWC 170) and aerobic capacity (peak V̇O₂) was evaluated in 6- to 8-year-old children (n = 18). The mean (± SD) peak V̇O₂ was 44.1 ± 5.6 ml • kg⁻¹ • min⁻¹. Peak V̇O₂ was not significantly different for children (n = 8) who had completed two treadmill trials (45.4 vs. 43.5 ml • kg⁻¹ • min⁻¹; R = 0.67, p<0.05). The log LSI expressed as counts per hour (M ± SD = 2.1 ±.22 cts/hr) was the only activity method significantly related to peak V̇O₂ (r = 0.59, p<0.05). The correlation between peak V̇O₂ with the questionnaire was positive but nonsignificant (r = 0.20). PWC 170 was not related to peak V̇O₂ (r = 0.21) or the activity variables (r = 0.12 questionnaire; r = 0.18 log LSI). When the group was divided into high and low peak V̇O₂ groups (high: M = 48.8 ml • kg⁻¹ • min⁻¹; low: M = 39.5 ml • kg⁻¹ • min⁻¹), the log LSI was able to distinguish significant differences in activity levels (high: 2.23 ±. 19 cts/hr; low: 1.99±.19 cts/hr). This study suggests that activity measured with the LSI and aerobic capacity are related in this sample of 6- to 8-year-old children.