Differences in demographic, behavioral, and biological variables between those with valid and invalid accelerometry data: implications for generalizability.

BACKGROUND: The exclusion of participants with invalid accelerometry data (IAD) may lead to biased results and/or lack of generalizability in large population studies. The purpose of this study was to investigate whether demographic, behavioral, and biological differences occur between those with IAD and valid accelerometry data (VAD) among adults using a representative sample of the civilian noninstitutionalized U.S. population. METHODS: Ambulatory participants from NHANES (2003-2004) who were 20-85 years of age were included in the current study and wore an ActiGraph 7164 accelerometer for 7 days. A "valid person" was defined as those with 4 or more days of at least 10+ hrs of monitoring per day. Among adults (20-85 yrs), 3088 participants provided VAD and 987 provided IAD. Demographic, behavioral, and biological information were obtained from the household interview or from data obtained in a mobile examination center. RESULTS: Differences were observed in age, BMI, ethnicity, education, smoking status, marital status, use of street drugs, current health status, HDL-cholesterol, C-reactive protein, self-reported vigorous physical activity, and plasma glucose levels between those with VAD and IAD. CONCLUSIONS: Investigators should take into consideration the potential cut-off bias in interpreting results based on data that excludes IAD participants.

Group training in adolescent runners: influence on VO2max and 5-km race performance.

The aims of this study were to (a) examine the interrelationships between training intensity, VO2max, and race performance in adolescent crosscountry runners and (b) determine if adolescent runners participating in a group crosscountry training program differ in the amount of training time at various intensities. In this study, 7 adolescent runners performed a laboratory-based VO2max test before and after a 9-week high-school crosscountry season. Heart rate (HR) and ventilatory threshold (VT) were used to identify 3 training zones for each runner based on the HR at ventilator threshold (HR(VT)): zone 1: >15 b·min(-1) below HR(VT); zone 2: between zone 1 and HR(VT); zone 3: >HR(VT). During each training session throughout the season, HR was measured to quantify the amount of training time in each of these 3 intensity zones. Results showed that the time in each of the 3 zones was not significantly associated with 5-km race performance. Zone 3 training time was positively associated with postseason VO2max (r = 0.73, p = 0.06); VO2max was significantly inversely associated with 5-km race performance (r = -0.77, p = 0.04). Each week, the amount of training time at, above, and below the VT was significantly different among the participants even though the training prescription for the group was standardized. The results suggest that, among adolescent crosscountry runners, training above the VT may be important in increasing VO2max and ultimately, race performance. Given the between-participant differences in the amount of training time in each HR zone, coaches should apply individual, rather than group, training programs.

Physiological adaptations and analysis of training content in high school cross-country runners.

The purposes of this study were to examine effects of a season of training on aerobic performance in cross-country distance runners and to analyze the training using subjective and objective techniques. Subjects averaged 184 minutes of running per week, with 45%, 24%, and 31% occurring in zones below, near, and above the heart rate (HR) corresponding to ventilatory threshold (VT(HR)), respectively (Zone 1: HR > 15 bpm below VT(HR); Zone 2: HR between Zone 1 and VT(HR); Zone 3: HR > VT(HR)). Maximal oxygen uptake (VO(2 max)) increased by 5.1%, 5-km race time by 46 seconds (3.7%), and 2-km time trial performance by 54 seconds (10.7%) from pre- to postseason. Results are similar to previous research demonstrating that short-term (< 3 months) endurance training elicits improvements in various physiological parameters. Findings were not consistent with previous research that suggests a discrepancy may exist between the runners' perceptions and the physiological effects of their training.