Medicine and Science in Sports and Exercise

Purpose: This study examined the effects of different pressure threshold inspiratory loads on lactate clearance and plasma acid–base balance during recovery from maximal exercise. Methods: Eight moderately trained males (V ˙ O 2peak = 4.29 T 0.46 LImin j1) performed, on different days, four maximal incremental cycling tests (power started at 0 W and increased by 20 WImin j1) of identical duration (exercise time during the first trial was 16.32 T 1.12 min). During 20-min recovery, subjects either rested passively or breathed through a constant pressure threshold inspiratory load of 10 (ITL10), 15 (ITL15), or 20 (ITL20) cm H 2 O. Plasma lactate concentration ([La j ]) was measured, and acid–base balance was quantified using the physicochemical approach, which describes the dependency of [H + ] on the three independent variables: strong ion difference ([Na + ] + [K + ] j [Cl j ] + [La j ]), the total concentration of weak acids, and the partial pressure of carbon dioxide. Results: Peak exercise responses were not significantly different between trials. During recovery, the area under the plasma [La j ] curve was not different between trials (pooled mean = 261 T 60 mEq) and the [La j ] measured at the end of the 20-min recovery was also similar (passive recovery = 9.2 T 3.1 mEqIL j1 , ITL10 = 9.3 T 3.1 mEqIL j1 , ITL15 = 8.7 T 2.8 mEqIL j1 , ITL20 = 8.7 T 3.2 mEqIL j1). Similarly, changes in other strong ions contributing to strong ion difference and total concentration of weak acids, partial pressure of carbon dioxide, and, therefore, [H + ] were not different between trials. Conclusions: These data suggest that, in individuals of moderate endurance training status, inspiratory loading at the intensities used in the present study does not accelerate lactate clearance or modify plasma acid–base balance during recovery from maximal exercise.

Purpose: U.S. high school athletes sustain millions of injuries annually. Detailed patterns of knee injuries, among the most costly sports injuries, remain largely unknown. We hypothesize that patterns of knee injuries in U.S. high school sports differ by sport and sex. Methods: U.S. high school sports-related injury data were collected for 20 sports using the National High School Sports-Related Injury Surveillance System, High School RIO™. Knee injury rates, rate ratios (RR), and injury proportion ratios were calculated. Results: From 2005/2006 to 2010/2011, 5116 knee injuries occurred during 17,172,376 athlete exposures (AE) for an overall rate of 2.98 knee injuries per 10,000 AE. Knee injuries were more common in competition than in practice (rate ratio = 3.53, 95% confidence interval [CI] = 3.34-3.73). Football had the highest knee injury rate (6.29 per 10,000 AE) followed by girls' soccer (4.53) and girls' gymnastics (4.23). Girls had significantly higher knee injury rates than boys in sex-comparable sports (soccer, volleyball, basketball, baseball/softball, lacrosse, swimming and diving, and track and field; RR = 1.52, 95% CI = 1.39-1.65). The most commonly involved structure was the medial collateral ligament (reported in 36.1% of knee injuries), followed by the patella/patellar tendon (29.5%), anterior cruciate ligament (25.4%), meniscus (23.0%), lateral collateral ligament (7.9%), and posterior cruciate ligament (2.4%). Girls were significantly more likely to sustain anterior cruciate ligament injuries in sex-comparable sports (RR = 2.38, 95% CI = 1.91-2.95). Overall, 21.2% of knee injuries were treated with surgery; girls were more often treated with surgery than boys in sex-comparable sports (injury proportion ratio = 1.30, 95% CI = 1.11-1.53). Conclusions: Knee injury patterns differ by sport and sex. Continuing efforts to develop preventive interventions could reduce the burden of these injuries.

The purpose of this Position Stand is to provide an overview of issues critical to understanding the importance of exercise and physical activity in older adult populations. The Position Stand is divided into three sections: Section 1 briefly reviews the structural and functional changes that characterize normal human aging, Section 2 considers the extent to which exercise and physical activity can influence the aging process, and Section 3 summarizes the benefits of both long-term exercise and physical activity and shorter-duration exercise programs on health and functional capacity. Although no amount of physical activity can stop the biological aging process, there is evidence that regular exercise can minimize the physiological effects of an otherwise sedentary lifestyle and increase active life expectancy by limiting the development and progression of chronic disease and disabling conditions. There is also emerging evidence for significant psychological and cognitive benefits accruing from regular exercise participation by older adults. Ideally, exercise prescription for older adults should include aerobic exercise, muscle strengthening exercises, and flexibility exercises. The evidence reviewed in this Position Stand is generally consistent with prior American College of Sports Medicine statements on the types and amounts of physical activity recommended for older adults as well as the recently published 2008 Physical Activity Guidelines for Americans. All older adults should engage in regular physical activity and avoid an inactive lifestyle.

It is the position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine that physical activity, athletic performance, and recovery from exercise are enhanced by optimal nutrition. These organizations recommend appropriate selection of foods and fluids, timing of intake, and supplement choices for optimal health and exercise performance. This updated position paper couples a rigorous, systematic, evidence-based analysis of nutrition and performance-specific literature with current scientific data related to energy needs, assessment of body composition, strategies for weight change, nutrient and fluid needs, special nutrient needs during training and competition, the use of supplements and ergogenic aids, nutrition recommendations for vegetarian athletes, and the roles and responsibilities of the sports dietitian. Energy and macronutrient needs, especially carbohydrate and protein, must be met during times of high physical activity to maintain body weight, replenish glycogen stores, and provide adequate protein to build and repair tissue. Fat intake should be sufficient to provide the essential fatty acids and fat-soluble vitamins and to contribute energy for weight maintenance. Although exercise performance can be affected by body weight and composition, these physical measures should not be a criterion for sports performance and daily weigh-ins are discouraged. Adequate food and fluid should be consumed before, during, and after exercise to help maintain blood glucose concentration during exercise, maximize exercise performance, and improve recovery time. Athletes should be well hydrated before exercise and drink enough fluid during and after exercise to balance fluid losses. Sports beverages containing carbohydrates and electrolytes may be consumed before, during, and after exercise to help maintain blood glucose concentration, provide fuel for muscles, and decrease risk of dehydration and hyponatremia. Vitamin and mineral supplements are not needed if adequate energy to maintain body weight is consumed from a variety of foods. However, athletes who restrict energy intake, use severe weight-loss practices, eliminate one or more food groups from their diet, or consume unbalanced diets with low micronutrient density may require supplements. Because regulations specific to nutritional ergogenic aids are poorly enforced, they should be used with caution and only after careful product evaluation for safety, efficacy, potency, and legality. A qualified sports dietitian and, in particular, the Board Certified Specialist in Sports Dietetics in the United States, should provide individualized nutrition direction and advice after a comprehensive nutrition assessment.

Exogenous fructose 1,6-diphosphate (FDP), a glycolytic intermediate, has recently been demonstrated to accelerate ATP production, prevent glycogen breakdown, stimulate glycogen synthesis, and synthesize free fatty acids in animals and humans. To assess the effects of FDP on the hormonal and metabolic response to exercise, ten trained males (34 +/- 7 yr) underwent 1 h of continuous exercise at 70% VO2max followed by 20 W.min-1 increments to exhaustion. Two hundred fifty mg.kg-1 body weight FDP or placebo was infused in randomized, double-blind, crossover fashion. No differences were observed in heart rate, blood pressure, gas exchange data, perceived effort, or glucose, insulin, free fatty acid, lactate, beta-hydroxybutyrate, glycerol, and glucagon concentration at rest, during exercise, or upon exhaustion. In contrast to the previously reported bioenergetic effects of FDP under conditions in which glycolysis is impeded (acidosis, hypoxia, and ischemia), FDP did not affect the gas exchange, hormonal, or substrate response to moderately high intensity exercise in healthy normals.

The logical validity of a 1.5-mile run as a measure of aerobic capacity, and the validity of Borg's laboratory model of perceived exertion (RPE) were examined in a field setting on a 440-yd cinder track. Performance time, heart rate (HR), and RPE were described for college-age males (N=67) instructed to achieve the lowest time possible during an "all-out" effort. Alpha and canonical factor analyses revealed three robust factors for performance times: 1) lap 1, 2) laps 2.5, 3) lap 6; two robust factors for HR: 1) laps 3-6, 2) laps 1 and 2; and four factors for RPE: 1) lap 6, 2) laps 1-3, 3) laps 4 and 5, 4) first 220 yd of lap 1. Results indicated distinct pacing characteristics of an initial sprint, a stable speed reduction, and a finishing sprint. This pace was generally independent of Ss HR (r's, mean lap 1 = 0.09; mean laps 2-5 = 0.19, mean lap 6 = 0.21) and RPE (r's, mean lap 1 = -0.15; mean laps 2-5 = 0.12; mean lap 6 = 0.07), and in part these findings at least implicate confounding influences by anaerobic metabolism and Ss motivation on performance. This possibility was supported by the fact that 95% of performance variance could be accounted for by pace factors of the initial and finishing sprints. Both HR and RPE response followed a linear-like increase as a function of cumulative time and distance. However, only a small relationship between HR and RPE (r, mean = 0.16) was observed during the run, and the obtained correlations did not support a central RPE-control model based on cardiovascular stress.

There is little evidence supporting sustainability of public health interventions based upon the 10,000 steps concept conducted in "real-world" settings. This study investigated the effectiveness of the 10,000 Steps Walking Challenge, initiated in conjunction with the 2006 Commonwealth Games in Melbourne, Australia, in March 2006. This study analyzed characteristics of registrants (n = 1836), pedometer counts logged onto a Web site between February 2006 and February 2007 (n = 18,032 entries by 914 participants), and two surveys of participants in June 2006 (n = 128) and December 2006 (n = 62). The program reached its target population of females aged 30-49 yr (40.2% of participants), a group known to have low activity levels, which also has potential to influence the behavior of family, friends, and workmates. Compliance was poor; only 49.8% of registrants ever logged steps, and of these, only 45.5% continued beyond the period of the challenge and 16.6% for more than 1 month. Mean (9527 +/- 297, 95% confidence interval) and median (9638) recorded steps per day came close to the target of 10,000 steps; 80.1% of participants reached 10,000 steps at least once and 21.9% did so every time they logged steps. For survey respondents who provided complete data (n = 53), the mean estimated daily steps increased significantly (P < 0.001) from 6401 +/- 884 steps before the program to 9921 +/- 1039 steps at the first survey and then fell back significantly (P = 0.026) to 8727 +/- 1284 steps at the second survey but remained significantly higher than the baseline figure (P < 0.001). The program had immediate effectiveness and was sustainable for a small proportion of participants, but effectiveness was limited by problems with long-term motivation and compliance/adherence.

The purpose of this study was to discuss, in the light of the results of a survey, the calcium ration of a sample of French youth and to determine whether various sports activities can be related to dietary calcium intake. Physical activity was evaluated using Baecke's questionnaire. Calcium intake was evaluated using a food frequency oriented questionnaire. The survey was performed on a population of 10,373 subjects (6,966 males and 3,407 females) including three different groups of subjects: school children and college students, military personnel, and athletes registered in sports federations. The mean age of this population was 19 +/- 9 yr, ages ranging between 7 and 50 yr. The mean amount of declared calcium intake (DCI) for the total population was 1242 +/- 843 mg per 24 hr (mg x d(-1)). Fifty percent of this population consumed less than 1000 mg x d(-1) and 13% less than 500 mg x d(-1). There was no significant relationship between the index of activity and declared calcium intake. Calcium intake decreased with age and was lower in females compared to males. The subjects trained in individual endurance sports such as triathlon, biking, and road running have a lower DCI than subjects trained in team sports such as volley ball, handball, or basketball. This survey, performed on a large population, does indicate that for half of them daily calcium intake is below the threshold of 1,000 mg x d(-1) considered the daily requirement covering the needs of a population without age or gender distinction and that calcium intake is not related to the level of physical activity.

The study's purposes were to 1) assess changes in cardiorespiratory fitness (CRF) from 1998 to 2010, controlling for decimal age and body mass index (BMI), and 2) repeat the analysis in cohorts from 2005 to 2010, controlling for maturation, deprivation, and BMI. A total of 27,942 (n = 14,247 boys) 9- to 10.9-yr-old participants from one UK city were included in this serial cross-sectional study from 1998-1999 to 2009-2010. An indices of multiple deprivation (IMD) score was assigned to each participant on the basis of home postcode. Stature, sitting stature, and body mass were estimated. BMI and somatic maturity were calculated. Performance on the 20-m multistage shuttle run test (20mSRT) was used to estimate CRF (total shuttles). One-way ANCOVAs were completed to assess temporal trends in CRF, separately by sex. Model 1 assessed changes from 1998 to 2010 and included decimal age and BMI as covariates. Model 2 assessed changes from 2005 to 2010 and included maturity, IMD, and BMI as covariates. Results indicate that 20mSRT performance has declined in UK schoolchildren. An annual decline of 1.34% and 2.29% was observed in boys and girls, respectively. In model 1, for boys, the baseline cohort performed better than all other groups with the exception of the 1999-2000 group. For girls, declines in 20mSRT performance were observed from 2003 onward. In model 2, for boys, the 2007-2008 and 2008-2009 cohorts completed fewer 20mSRT shuttles than all other groups. For girls, the 2007-2008 and 2008-2009 cohorts also performed worse than all other years. The decline in CRF suggests children in the more recent SportsLinx cohorts may be at an increased risk of cardiometabolic illness in comparison with earlier cohorts. The promotion of vigorous physical activity is urged to promote CRF in children.

Exercise alone or in combination with environmental heat stress can elevate blood S-100beta protein concentrations. However, the explanatory power of exercise with marked environmental heat stress on the appearance of S-100beta is questionable. It is possible that the process of heat acclimation might afford additional insight. Determine the S-100beta response to moderate-intensity exercise with heat strain before and after heat acclimation. Nine healthy male volunteers completed 10 consecutive days of heat acclimation consisting of up to 100 min of treadmill walking (1.56 m x s(-1), 4% grade) in the heat (45 degrees C, 20% relative humidity). Changes in HR, rectal temperature (T(re)), and sweat rate (SR) were examined to determine successful acclimation. Area under the curve (AUC) for T(re) greater than 38.5 degrees C was calculated to assess cumulative hyperthermia. Blood samples were taken before and after exercise on days 1 and 10 and were analyzed for serum osmolality and S-100beta concentration. All subjects displayed physiological adaptations to heat acclimation including a significant (P < 0.05) reduction in final HR (161 to 145 bpm) and T(re) (39.0 to 38.4 degrees C), as well as a modest (approximately 10%) increase in SR (1.10 to 1.20 L x h(-1); P = 0.09). No differences were observed in pre- to postexercise serum S-100beta concentrations on day 1 or 10, and no differences were observed in S-100beta values between days 1 and 10. No significant correlations were found between S-100beta values and any variable of interest. S-100beta concentrations do not necessarily increase in response to exercise-heat strain, and no effect of heat acclimation on S-100beta could be observed despite other quantifiable physiological adaptations.

The aim of the present study was to assess the risk factors for magnetic resonance imaging (MRI)-detected bone stress injuries in the pelvis, hip, thigh, and knee in a large cohort of Finnish conscripts during a follow-up of 102,515 person-years. An epidemiologic prospective cohort study of 152,095 conscripts, including 2345 (1.5%) females, was conducted. Localized pain in the pelvis, hip, thigh, or knee resulted in an orthopedic surgeon's consultation and subsequent MRI examination at the Central Military Hospital, Helsinki, Finland. Risk factors were systematically collected from 1998 to 2004, including data on conscripts' physical fitness and body composition measured at the beginning of their military service. Altogether, 319 MRI-detected bone stress injuries of the pelvis, hip, thigh, or knee were identified in our cohort; thus, the incidence was 311 (95% CI: 277-345) per 100,000 person-years. The female:male ratio varied substantially, depending on the anatomic location of the injury; it was highest for sacral injuries (female:male ratio = 51.1) and lowest for injuries of the femoral condyle (female:male ratio = 0.8). In univariate Cox regression analysis, poor muscle strength and a poor result in a 12-min run were significantly associated with bone stress injuries. In multivariable analysis, the strongest risk factors for bone stress injuries were female gender (hazard ratio 8.2; 95% CI: 4.8-14.2) and higher age (hazard ratio 2.1; 95% CI: 1.4-3.1). Female military trainees have a highly increased risk of bone stress injuries of the pelvis and hip compared with male conscripts. Sacral stress fractures are typical bone stress injuries in female military recruits. Physicians should remember the possibility of bone stress injury, especially when examining stress-related pain symptoms of the pelvic area in physically active young adult females.

The high prevalence of obesity in Western societies has been attributed in part to high-fat low-CHO food consumption. However, people have also become less active, and inactivity may have increased the risk for weight gain from poor dietary choices. Analyses were performed to test whether diet-weight relationships were attenuated by vigorous exercise. Age- and education-adjusted cross-sectional regression analyses of 62,042 men and 44,695 women recruited for the National Runners' Health Study were conducted. Reported meat and fruit intakes were analyzed separately and as indicators of high-risk diets. The runners were generally lean (mean ± SD: males = 24.15 ± 2.81 kg·m(-2), females = 21.63 ± 2.70 kg·m(-2)) as measured by body mass index (BMI), educated (males = 16.42 ± 2.47 yr, females = 16.04 ± 2.32 yr), and middle-aged (males = 44.40 ± 10.83 yr, females = 38.21 ± 10.08 yr), who ran 5.30 ± 3.23 km·d(-1) if male and 4.79 ± 3.00 km·d(-1) if female. Running significantly attenuated BMI's relationship to reported meat and fruit intakes in men (P < 10(-8) and P < 10(-12), respectively) and women (P < 10(-15) and P < 10(-6), respectively). Specifically, compared with running <2 km·d(-1), running >8 km·d(-1) reduced the apparent BMI increase per serving of meat by 43% in men (slope ± SE = from 0.74 ± 0.10 to 0.42 ± 0.06) and 55% in women (from 1.26 ± 0.13 to 0.57 ± 0.09) and reduced the apparent BMI reduction per serving of fruit by 75% in men (from -0.28 ± 0.04 to -0.07 ± 0.02) and 94% in women (from -0.16 ± 0.05 to -0.01 ± 0.02). Running also significantly attenuated the concordant relationship between reported meat intake and waist and chest circumferences in men (P < 10(-9) and P = 0.0002, respectively) and women (P = 0.0004 and P < 10(-5), respectively) and the concordant relationship between meat intake and hip circumference in women (P < 10(-6)). Vigorous exercise may mitigate diet-induced weight gain, albeit not guaranteeing protection from poor dietary choices.