Comparison of Muscle Activation Between Back Squats and Belt Squats.

Evans, TW, McLester, CN, Howard, JS, McLester, JR, and Calloway, JP. Comparison of muscle activation between back squats and belt squats. J Strength Cond Res 33(7S): S52-S59, 2019-A machine belt squat is a piece of equipment designed to allow the performance of squats while loading weight on the lifter's hips using a belt. The purpose of this investigation was to determine whether belt squats differ from back squats in activation of the primary movers and to determine the predictive capabilities of back squat load, training status, and anthropometric data on belt squat load. Thirty-one participants (16 men and 15 women) completed anthropometric measurements, a demographic questionnaire, a familiarization visit, and 2 testing visits, completing a 5 repetition maximum test for back squat and belt squat. Surface electromyography was used to measure muscle activation for the left and right vastus medialis, vastus lateralis, rectus femoris, and gluteus maximus (GM). Comparison of muscle activation between the 2 exercises showed significant differences in the left GM (back squat: 0.84 ± 0.45, belt squat: 0.69 ± 0.22, p = 0.015) and right GM (back squat: 0.86 ± 0.45, belt squat: 0.71 ± 0.29, p = 0.004). Regression analysis computed significant prediction equations for belt squat load for general population, men, women, and advanced lifters. Overall, results indicate that belt squats may significantly differ in GM activation from back squats. Back squat load, as well as other variables, may be effective in accurately estimating appropriate belt squat load. These findings may help to more appropriately program for training with machine belt squats as a back squat alternative.

Central Hemodynamics Measured During 5 Repetition Maximum Free Weight Resistance Exercise.

The PhysioFlow™ is a piece of equipment that uses bioimpedance cardiography to measure central hemodynamics. The purpose of this research was to explore the novel approach of monitoring central hemodynamics during free weight resistance exercise using bioimpedance cardiography throughout a 5 repetition maximum (5RM). Thirty participants ranging from beginner to advanced lifters (16 males and 14 females) completed a 5RM for back squat, seated push press, and bicep curl while connected to the PhysioFlow™ to assess the response of heart rate (HR), stroke volume (SV), cardiac output (Q), and ejection fraction (EF). Participants were cued for form and to breathe normally throughout the lifts. The PhysioFlow™ detected an increase in HR and Q for all lifts between rest and each repetition (p < 0.05). There was also an increase in HR and Q from repetition 1 to repetition 5 for all lifts (p < 0.05). No changes in EF or SV were detected between resting measurements and each repetition for all lifts (p > 0.05) and no changes in EF or SV were detected when all repetitions were compared to each other for all lifts (p > 0.05). In conclusion, the PhysioFlow™ was able to detect changes in HR and Q during dynamic free weight resistance exercise. This novel approach may provide a mechanism for monitoring central hemodynamics during free weight resistance training. However, more research needs to be conducted as the exercise protocol for this investigation did not allow for a comparison to a reference method.

Comparison of obesity assessment procedures in obese African-American and white women.

The purpose of this study was to compare the accuracy of dual energy X-ray absorptiometry (DEXA) to field-based procedures for the estimation of obesity in 27 sedentary and obese African-American (AA) (34.8, +/- 7.7 yr) and 25 sedentary and obese White women (41.1, +/- 8.3 yr). Body fat was estimated by DEXA and skinfolds equations. Obesity was also estimated from BMI and percent of ideal body weight (greater than 120% of ideal body weight based on height and weight tables). All of the procedures classified the subjects as obese. Results from each procedure were compared with minimal obesity standards to determine the percentage by which each mean exceeded the minimal standard (percent difference). The percent difference was smaller for BMI and percent ideal body weight than for the 2 body fat assessment procedures. Although DEXA percent body fat did not differ by race, BMI and percent ideal body weight tended to be greater in AA women compared to White women, and more AA women were classified as obese. Therefore, field-based procedures that do not include percent body fat assessments are not as accurate for AA women. This finding suggests that obesity can be more effectively assessed in AA women if the standards for classifications are population-specific.