Construct Validity, Test-Retest Reliability, and Repeatability of Performance Variables Using a Flywheel Resistance Training Device.

Bollinger, LM, Brantley, JT, Tarlton, JK, Baker, PA, Seay, RF, and Abel, MG. Construct validity, test-retest reliability, and repeatability of performance variables using a flywheel resistance training device. J Strength Cond Res 34(11): 3149-3156, 2020-Power production is highly associated with physical performance; however, the ability to quantitatively measure power output during resistance exercise is lacking. The purpose of this study was to determine the validity and test-retest reliability of flywheel-based performance testing. Twelve young, resistance trained subjects completed 2 bouts of resistance exercise using a flywheel resistance training device (Exxentric kbox 4 Pro). Each session consisted of 3 sets of 3 exercise (bent-over row, Romanian deadlift, and biceps curl) with varying moments of inertia (0.050, 0.075, and 0.100 kg·m, respectively) in random order. Each set consisted of 5 maximal effort repetitions with 3-minute recovery between sets. Average power, peak concentric and eccentric power, average force, average speed, and total work for each set were recorded. Regression analysis revealed a near-perfect relationship between measured and predicted power, force, and work at given workloads. Pearson's r between trials 1 and 2 revealed good (≥0.70) to excellent (≥0.90) test-retest reliability for all outcomes with the exception of peak eccentric power for biceps curls (r = 0.69), which narrowly missed the cutoff for acceptable reliability. Bland-Altman plots revealed small (approximately 5-15%), but statistically significant bias between the 2 trials for some measures. Coefficient of repeatability for all outcomes was relatively high, indicating poor repeatability. Flywheel-based performance testing provides valid data. However, reliability varies between individual lifts and specific outcomes. Given the poor repeatability between trials, it is likely that subjects who are unaccustomed to this modality may require multiple testing sessions or a thorough familiarization period to ensure accurate measures of power, force, speed, and work during flywheel-based performance testing.

Knee extensor torque and BMI differently relate to sit-to-stand strategies in obesity.

BACKGROUND: Obesity alters whole body kinematics during activities of daily living such as sit-to-stand (STS), but the relative contributions of excess body mass and decreased relative strength are unknown. METHODS: Three-dimensional motion analysis data was collected on 18 obese subjects performing sit-to-stand (chair height: 52 cm). Isometric knee extensor strength was measured at 900 knee flexion. Forward stepwise linear regression was used to determine the association between the independent variables BMI and the knee extensor torque with the dependent variables: foot position and trunk kinematics. FINDINGS: BMI, but not knee extensor torque, was inversely related to shank angle and positively related to stance width. Relative knee extensor torque, but not BMI, was inversely associated with initial trunk angle, peak trunk flexion angle, and peak trunk extension velocity (r2 = 0.470-0.495). BMI was positively associated with peak trunk flexion velocity, but no other parameters of trunk kinematics. In the final regression model, BMI was the primary predictor (r2 = 0.423) and relative knee extensor strength served as a secondary predictor (r2 = 0.118) of peak trunk flexion velocity. INTERPRETATION: BMI and knee extensor strength differently contribute to sit-to-stand performance strategies in obese subjects. Muscle strength may be an important determinant of whole-body kinematics during activities of daily living such as STS.

Reliability and validity of various laboratory methods of body composition assessment in young adults.

Accurate measures of body composition (BC) are essential for performance and health. In addition to accuracy, BC measures should be practical and be minimally invasive to maximize their utility. The purpose of the present study was to compare the day-to-day variability and validity of four common laboratory-based body composition assessments to a criterion four-compartment model. Dual x-ray absorptiometry (DXA), air displacement plethysmography (BP), multi-frequency bioelectrical impedance (MF-BIA) and underwater weighing (UWW) were performed twice in a sample of 32 young men and women. Participants were assessed in a fasted, euhydrated state 2-7 days apart. All methods were compared to a criterion four-compartment model using BP-derived body volume, DXA-derived bone mineral content and MF-BIA-derived total body water (4CBP ). Additional four-compartment models using UWW- and DXA-derived body volume were also examined (4CUWW ) and (4CDXA ). Validity results were conducted with paired t-tests and Bland-Altman analysis. Reliability was determined using intraclass correlations (ICC), coefficients of variation (CV) and standard error of the measurement (SEM). Validity analysis revealed that all methods overestimated per cent body fat and fat mass, and underestimated fat-free mass when compared with 4CBP , but only DXA and BP were significantly different (P<0·008). All measures were highly reliable across days (ICCs > 0·9, CVs < 12%). Results of the present study indicate that typical laboratory-based methods of body composition are valid and reliable. However, we caution that results should not be translated between methods and assessments should be performed with the same instrument when the goal is to monitor changes in body composition over time.

Energy compensation after sprint- and high-intensity interval training.

BACKGROUND: Many individuals lose less weight than expected in response to exercise interventions when considering the increased energy expenditure of exercise (ExEE). This is due to energy compensation in response to ExEE, which may include increases in energy intake (EI) and decreases in non-exercise physical activity (NEPA). We examined the degree of energy compensation in healthy young men and women in response to interval training. METHODS: Data were examined from a prior study in which 24 participants (mean age, BMI, & VO2max = 28 yrs, 27.7 kg•m-2, and 32 mL∙kg-1∙min-1) completed either 4 weeks of sprint-interval training or high-intensity interval training. Energy compensation was calculated from changes in body composition (air displacement plethysmography) and exercise energy expenditure was calculated from mean heart rate based on the heart rate-VO2 relationship. Differences between high (≥ 100%) and low (< 100%) levels of energy compensation were assessed. Linear regressions were utilized to determine associations between energy compensation and ΔVO2max, ΔEI, ΔNEPA, and Δresting metabolic rate. RESULTS: Very large individual differences in energy compensation were noted. In comparison to individuals with low levels of compensation, individuals with high levels of energy compensation gained fat mass, lost fat-free mass, and had lower change scores for VO2max and NEPA. Linear regression results indicated that lower levels of energy compensation were associated with increases in ΔVO2max (p < 0.001) and ΔNEPA (p < 0.001). CONCLUSIONS: Considerable variation exists in response to short-term, low dose interval training. In agreement with prior work, increases in ΔVO2max and ΔNEPA were associated with lower energy compensation. Future studies should focus on identifying if a dose-response relationship for energy compensation exists in response to interval training, and what underlying mechanisms and participant traits contribute to the large variation between individuals.

Impact of 4 weeks of interval training on resting metabolic rate, fitness, and health-related outcomes.

Resting metabolic rate (RMR) and substrate oxidation (respiratory exchange ratio; RER) are important indicators of health. The effects of interval training on RMR have not been thoroughly investigated, which was the purpose of the present study. Thirty men and women (mean ± SD age and maximal oxygen uptake: 28.8 ± 7.6 years and 33.0 ± 8.3 mL·kg-1·min-1) completed 4 weeks of Wingate-based sprint interval training (SIT), repeated 1-min high-intensity intervals (HIIT), or served as controls. Before and after training, RMR, resting RER, maximal oxygen uptake, body composition, physical activity, and energy intake were recorded. Data were analyzed using a repeated-measures ANOVA. RMR increased in response to 4 weeks of SIT training (1789 ± 293 to 1855 ± 320 kcal·day-1; p = 0.003) but did not increase after HIIT (1670 ± 324 to 1704 ± 329 kcal·day-1; p = 0.06). While SIT increased RMR by ∼2× the magnitude of HIIT, the difference was not significant (p = 0.5). Fasting substrate oxidation and RER did not change (p > 0.05). Maximal oxygen uptake increased, and small changes were also observed in percent body fat and fat mass (p < 0.05 for all). In conclusion, SIT provided a time-efficient stimulus to increase RMR after 4 weeks in healthy adults. However, the clinical relevance of the changes observed in this study remains to be determined. Further studies should be conducted in obese individuals and those with diabetes or insulin resistance to examine if interval training (≥4 weeks) influences resting metabolic rate in magnitudes similar to that reported here.

Caffeine, coffee, and appetite control: a review.

Coffee and caffeine consumption has global popularity. However, evidence for the potential of these dietary constituents to influence energy intake, gut physiology, and appetite perceptions remains unclear. The purpose of this review was to examine the evidence regarding coffee and caffeine's influence on energy intake and appetite control. The literature was examined for studies that assessed the effects of caffeine and coffee on energy intake, gastric emptying, appetite-related hormones, and perceptual measures of appetite. The literature review indicated that coffee administered 3-4.5 h before a meal had minimal influence on food and macronutrient intake, while caffeine ingested 0.5-4 h before a meal may suppress acute energy intake. Evidence regarding the influence of caffeine and coffee on gastric emptying, appetite hormones, and appetite perceptions was equivocal. The influence of covariates such as genetics of caffeine metabolism and bitter taste phenotype remain unknown; longer controlled studies are needed.