Purpose: Dietary nitrate supplementation has been reported to improve performance in kayaking and rowing exercise, which mandate significant recruitment of the upper-body musculature. Because the effect of dietary nitrate supplementation on swimming performance is unclear, the purpose of this study was to assess the effect of dietary nitrate supplementation on 100-m and 200-m swimming freestyle time-trial (TT) performance. Methods: In a double-blind, randomized crossover design, 10 moderately trained swimmers underwent 2 separate 3-d supplementation periods, with a daily dose of either 140 mL nitrate-rich (∼800 mg/d nitrate) or nitrate-depleted (PLA) beetroot juice (BRJ). After blood sampling on day 3, the swimmers performed both 200-m and 100-m freestyle swimming TTs, with 30 min recovery between trials. Results: Plasma nitrite concentration was greater after BRJ relative to PLA consumption (432  nmol/L, 111  nmol/L, respectively, P = .001). Systolic blood pressure was lowered after BRJ compared with PLA supplementation (114 , 120  mm Hg, respectively P = .001), but time to complete the 200-m (BRJ 152.6 [14.1] s, PLA 152.5 [14.1] s) and 100-m (BRJ 69.5 [7.2] s, PLA 69.4 [7.4] s) freestyle swimming TTs was not different between BRJ and PLA (P > .05). Conclusions: Although 3 d of BRJ supplementation increased plasma nitrite concentration and lowered blood pressure, it did not improve 100-m and 200-m swimming TT performance. These results do not support an ergogenic effect of nitrate supplementation in moderately trained swimmers, at least for 100-m and 200-m freestyle swimming performance.
Ozcan Esen, Ceri Nicholas, Mike Morris, and Stephen J. Bailey
Timothy F. Tyler, Brandon M. Schmitt, Stephen J. Nicholas, and Malachy P. McHugh
Hamstring-strain injuries have a high recurrence rate.
To determine if a protocol emphasizing eccentric strength training with the hamstrings in a lengthened position resulted in a low recurrence rate.
Longitudinal cohort study.
Sports-medicine physical therapy clinic.
Fifty athletes with hamstring-strain injury (age 36 ± 16 y; 30 men, 20 women; 3 G1, 43 G2, 4 G3; 25 recurrent injuries) followed a 3-phase rehabilitation protocol emphasizing eccentric strengthening with the hamstrings in a lengthened position.
Main Outcome Measures:
Injury recurrence; isometric hamstring strength at 80°, 60°, 40°, and 20° knee flexion in sitting with the thigh flexed to 40° above the horizontal and the seat back at 90° to the horizontal (strength tested before return to sport).
Four of the 50 athletes sustained reinjuries between 3 and 12 mo after return to sport (8% recurrence rate). The other 42 athletes had not sustained a reinjury at an average of 24 ± 12 mo after return to sport. Eight noncompliant athletes did not complete the rehabilitation and returned to sport before initiating eccentric strengthening in the lengthened state. All 4 reinjuries occurred in these noncompliant athletes. At time of return to sport, compliant athletes had full restoration of strength while noncompliant athletes had significant hamstring weakness, which was progressively worse at longer muscle lengths (compliance × side × angle P = .006; involved vs noninvolved at 20°, compliant 7% stronger, noncompliant 43% weaker).
Compliance with rehabilitation emphasizing eccentric strengthening with the hamstrings in a lengthened position resulted in no reinjuries.
Dylan Thompson, Clyde Williams, Stephen J. McGregor, Ceri W. Nicholas, Frank McArdle, Malcolm J. Jackson, and Jonathan R. Powell
The aim of the present study was to investigate whether 2 weeks of vitamin C supplementation affects recovery from an unaccustomed bout of exercise. Sixteen male subjects were allocated to either a placebo (P; n = 8) or vitamin C group (VC; n = 8). The VC group consumed 200 mg of ascorbic acid twice a day, whereas the P group consumed identical capsules containing 200 mg of lactose. Subjects performed a prolonged (90-min) intermittent shuttle-running test 14 days after supplementation began. Post-exercise serum creatine kinase activities and myoglobin concentrations were unaffected by supplementation. However, vitamin C supplementation had modest beneficial effects on muscle soreness, muscle function, and plasma concentrations of malondialdehyde. Furthermore, although plasma interleukin-6 increased immediately after exercise in both groups, values in the VC group were lower than in the P group 2 hours after exercise (p < .05). These results suggest that prolonged vitamin C supplementation has some modest beneficial effects on recovery from unaccustomed exercise.
Nicholas M. Edwards, Heidi J. Kalkwarf, Jessica G. Woo, Philip R. Khoury, Stephen R. Daniels, and Elaine M. Urbina
The objective of this study was to characterize the relationship between objectively-measured physical activity (PA) and cardiovascular risk factors in 7-year-old children and test the hypothesis that it differs by race.
Cross-sectional study of 308 7-year-old children drawn from a major US metropolitan community. PA (moderate-to-vigorous, MVPA; light, LPA; and inactivity, IA) was measured by accelerometry (RT3). Cardiovascular risk factors included BMI, blood pressure, and serum lipids, glucose and insulin concentrations. General linear modeling was used to evaluate the independent associations between PA measures and cardiovascular risk factors and interactions by race.
In black children, greater time spent in PA was independently associated with lower levels of triglycerides (MVPA and LPA, both p < .01), glucose (MVPA, p < .05), and insulin (MVPA, p < .01); these associations were not evident in white children. Across races, greater inactivity was independently associated with greater low-density lipoprotein cholesterol in overweight participants (p < .01) but not in normal weight participants. No PA measure was associated with BMI, systolic blood pressure, or high-density lipoprotein cholesterol.
In this cohort of 7-year-old children, the relationship between PA and some cardiovascular risk factors differed by race. These findings may have implications for targeting of PA promotion efforts in children.
Nicholas M. Edwards, Philip R. Khoury, Heidi J. Kalkwarf, Jessica G. Woo, Randal P. Claytor, and Stephen R. Daniels
Establishing and maintaining healthy physical activity (PA) levels is important throughout life. The purpose of this study was to determine the extent of PA tracking between ages 3 and 7 y. Objective measures of PA (RT3, triaxial accelerometer) were collected every 4 mo from ages 3–7; data from 234 children with PA measures available during each year of age were analyzed. Mean PA (total, moderate/vigorous (MV), and inactivity [IA]) was calculated for each year of age and adjusted for wear time. Correlations with age 3 PA were moderate at age 4 (r = .42−.45) but declined by age 7 (r = .19−.25). After classification into sex-specific tertiles of PA at age 3, boys in the high age 3 MVPA tertile maintained significantly higher PA at all subsequent ages, while girls in the high age 3 MVPA tertile were not significantly higher at age 6 and 7. Boys and girls in the high age 3 IA tertile had significantly higher IA at multiple subsequent years of age (p < .05 at ages 5 and 6). In conclusion, boys who were relatively more active at age 3 remained more active for several subsequent years. These findings highlight early-childhood differences in physical activity patterns between boys and girls.
Matthew Pearce, Tom R.P. Bishop, Stephen Sharp, Kate Westgate, Michelle Venables, Nicholas J. Wareham, and Søren Brage
Harmonization of data for pooled analysis relies on the principle of inferential equivalence between variables from different sources. Ideally, this is achieved using models of the direct relationship with gold standard criterion measures, but the necessary validation study data are often unavailable. This study examines an alternative method of network harmonization using indirect models. Starting methods were self-report or accelerometry, from which we derived indirect models of relationships with doubly labelled water (DLW)-based physical activity energy expenditure (PAEE) using sets of two bridge equations via one of three intermediate measures. Coefficients and performance of indirect models were compared to corresponding direct models (linear regression of DLW-based PAEE on starting methods). Indirect model beta coefficients were attenuated compared to direct model betas (10%–63%), narrowing the range of PAEE values; attenuation was greater when bridge equations were weak. Directly and indirectly harmonized models had similar error variance but most indirectly derived values were biased at group-level. Correlations with DLW-based PAEE were identical after harmonization using continuous linear but not categorical models. Wrist acceleration harmonized to DLW-based PAEE via combined accelerometry and heart rate sensing had the lowest error variance (24.5%) and non-significant mean bias 0.9 (95%CI: −1.6; 3.4) kJ·day−1·kg−1. Associations between PAEE and BMI were similar for directly and indirectly harmonized values, but most fell outside the confidence interval of the criterion PAEE-to-BMI association. Indirect models can be used for harmonization. Performance depends on the measurement properties of original data, variance explained by available bridge equations, and similarity of population characteristics.
Nicholas M. Edwards, Gregory D. Myer, Heidi J. Kalkwarf, Jessica G. Woo, Philip R. Khoury, Timothy E. Hewett, and Stephen R. Daniels
Evaluate effects of local weather conditions on physical activity in early childhood.
Longitudinal prospective cohort study of 372 children, 3 years old at enrollment, drawn from a major US metropolitan community. Accelerometer-measured (RT3) physical activity was collected every 4 months over 5 years and matched with daily weather measures: day length, heating/cooling degrees (degrees mean temperature < 65°F or ≥ 65°F, respectively), wind, and precipitation. Mixed regression analyses, adjusted for repeated measures, were used to test the relationship between weather and physical activity.
Precipitation and wind speed were negatively associated with total physical activity and moderate-vigorous physical activity (P < .0001). Heating and cooling degrees were negatively associated with total physical activity and moderate-vigorous physical activity and positively associated with inactivity (all P < .0001), independent of age, sex, race, BMI, day length, wind, and precipitation. For every 10 additional heating degrees there was a 5-minute daily reduction in moderatevigorous physical activity. For every additional 10 cooling degrees there was a 17-minute reduction in moderate-to-vigorous physical activity.
Inclement weather (higher/lower temperature, greater wind speed, more rain/snow) is associated with less physical activity in young children. These deleterious effects should be considered when planning physical activity research, interventions, and policies.