Citations

The primary purpose of this study was to examine the acute effects of a multi-ingredient preworkout supplement (MIPS) on isometric, concentric, and eccentric peak torque and electromyographic (EMG) responses of the leg extensors during a fatiguing isokinetic protocol. Thirteen male subjects (mean age ± SD = 22.9 ± 2.2 years) were assigned in crossover fashion to ingest an MIPS or placebo before an isokinetic protocol that consisted of 30 maximal, concentric and eccentric muscle actions with EMG signals recorded from the vastus lateralis, rectus femoris, and vastus medialis muscles. Immediately before (PRE) and after (POST) the isokinetic fatigue protocol, subjects were assessed for isometric peak torque. The MIPS condition resulted in greater isometric (205 ± 48 vs. 185 ± 44 N·m, p = 0.04) and concentric (121 ± 34 vs. 103 ± 27 N·m, p = 0.015) torque values versus placebo (collapsed across time). For eccentric peak torque as well as EMG amplitude and frequency values, there were no significant (p > 0.05) interactions or main effects for each condition. These findings indicated that acute ingestion of the MIPS enhanced isometric and concentric peak torque of the leg extensors, which was not explained by changes in the EMG signal.

Abstract Korpinen, M, Magee, M, Dulak-Sigler, C, Fields, JB, Jagim, AR, King, E, Burke, A, and Jones, MT. Seasonal changes in neuromuscular performance across a training year in women collegiate lacrosse athletes. J Strength Cond Res 39(11): 1186–1193, 2025—Body composition and athlete load management are vital to adequate training stimuli and to mitigate neuromuscular (NM) fatigue. Research is limited regarding NM performance (NMP) in women lacrosse athletes. Therefore, the purpose of this study was to investigate changes in NMP in women lacrosse athletes across a training year. Collegiate women lacrosse athletes ( n = 9, mean ± SD ; age = 19.1 ± 0.9 years, height = 168.4 ± 6.8 cm, body mass = 68.0 ± 8.1 kg) completed countermovement jump (CMJ) and isokinetic strength (IS) testing of dominant and nondominant legs 4 times throughout the season: preseason start, preseason end, in-season end, and off-season end to assess NMP. Measures included (a) CMJ output variables of reactive strength index modified (RSImod), jump height, relative values of braking force, peak power, peak propulsive force, impulse; (b) CMJ strategy variables of time-to-takeoff, eccentric duration, concentric duration, relative braking time, CMJ depth; and (c) IS relative peak torques of quadriceps and hamstrings musculature. Secondary measures including body composition variables of body mass, % body fat (%BF), and fat-free mass. Repeated measures ANOVA with Bonferroni post hoc analysis assessed changes in CMJ and IS parameters to determine patterns in NMP ( p < 0.05). Changes observed from preseason start to offseason end included increased CMJ depth ( p = 0.019), relative braking time ( p = 0.009), and %BF ( p = 0.01). The IS variables increased throughout the training year, except for a decrease during preseason, perhaps indicative of overreaching. Negative changes in alternative CMJ variables and body composition reduced NMP, which highlights the importance of off-season program design and implementation to elicit desired training adaptations.

Abstract VanZile, AW, Jones, DD, McHugh, LJ, Clickovich, GL, Morales, MA, Reimschisel, RK, Widenhoefer, TL, Baughman, JT, Urquidi, MD, Conner, DJ, Dobbs, WC, Jagim, AR, Luedke, JA, and Almonroeder, TG. Examining countermovement jump performance and dynamic balance among male high school athletes with varying levels of sports specialization. J Strength Cond Res 39(11): 1163–1168, 2025—Specializing at a young age may limit an athlete's motor development, since focusing on a single sport potentially exposes athletes to less variety of movements and neuromuscular demands. However, there are few studies examining the association between sport specialization and movement performance/control. The purpose of this study was to compare countermovement jump performance and dynamic balance among high school athletes of varying levels of sports specialization. 110 male high school athletes completed countermovement jump testing and the Y-Balance Test (YBT). Ground reaction forces were recorded during countermovement jumps and used to derive peak force, peak velocity, peak power, jump height, and the modified reactive strength index. Y-Balance Test composite scores were calculated to assess dynamic balance across multiple directions, for the dominant and non-dominant limbs. Athletes were grouped into high ( n = 46), moderate ( n = 39), and low ( n = 25) specialization groups based on their sport participation habits. There were no between-group differences for any of the countermovement jump metrics ( p > 0.05). For the YBT composite scores, there was not a group-by-limb interaction effect ( p = 0.28); however, there was a main effect of group ( p = 0.03). Post hoc tests indicated that the high specialization group exhibited lower YBT composite scores compared to the moderate specialization group ( p = 0.01) and a trend toward lower scores compared to the low specialization group ( p = 0.05). In general, highly specialized male athletes exhibited poorer dynamic balance compared to less specialized athletes.

Objectives The purpose of the current study was to evaluate differences in total sleep time and heart rate variability (HRV) in active-duty firefighters between on-shift and off-shift days. Methods 59 structural firefighters (age: 37.3±7.3 years; height: 1.80±0.08 m; weight: 88.9±14.1 kg and body mass index (BMI): 27.5±4.1 kg/m2) participated in this longitudinal observation study. Each morning for 15 weeks, firefighters were asked to sync a smart ring with a smartphone application to download night-time data, which were then extracted to a cloud-based software application for later analysis. The software also computed a readiness score each morning. All day types were coded as on-shift or off-shift. Results The average nightly sleep time for all firefighters was 6.95±1.24 hours. When off-shift, firefighters recorded more sleep compared with on-shift nights (off-shift: 6.97±0.50 hours vs on-shift: 6.68±0.52 hours; p<0.0001). HRV (p<0.0001) and readiness scores (p=0.02) were lower off-shift compared with on-shift. For the lagged correlation analysis, total sleep time was moderately positively correlated with the following day’s readiness score. Conclusions Firefighters recorded more total sleep time when off-shift compared with on-shift; however, HRV and readiness scores were higher on-shift. The lag-time correlations indicate an association between sleep time and HRV or readiness scores, with approximately half of the variability in readiness being attributable to changes in total sleep time, which highlights the complexity of the readiness and HRV signals/systems.

Abstract Dobbs, WC, Almonroeder, TG, Carpenter, M, Schmitt, RE, Jacobson, AK, Luedke, JA, Roberts, BM, and Jagim, AR. Relationships between the Army Combat Fitness Test scoring structure and laboratory measurements of physical fitness in reserve officer training corps cadets. J Strength Cond Res 39(7): 798–808, 2025—The Army Combat Fitness Test (ACFT) assesses aerobic and anaerobic fitness capabilities in the U.S. Army. The aim of this study was to evaluate the association between raw and composite ACFT scores and laboratory-based measurements of fitness. Nineteen Reserve Officers' Training Corp cadets performed a battery of laboratory-based fitness testing. Tests included a movement screening (Fusionetics), countermovement jumps, and maximal isometric mid-thigh pulls on portable force plates to determine power and strength. A Wingate test involving maximal cycling for 30 seconds was used to determine peak and mean power. On a separate day, cadets completed body composition and a graded exercise test on a motorized treadmill to determine peak oxygen uptake (V̇ o 2 peak). Pearson correlations and partial corrections with 2000 bootstraps were used to compare ACFT scores (raw, composite, gender-neutral composite, and z -scores) with laboratory results. Significant associations were identified as 95% confidence intervals, not including zero. The results indicated that V̇ o 2 peak ( r = 0.61, [0.08–0.84]), body fat percentage ( r = −0.4, [−0.72 to −0.06]), and relative peak power ( r = 0.38, [0.02–0.68]) were associated with the total ACFT composite score when partialled by sex. All laboratory tests, except the movement screening, showed meaningful associations with total ACFT z -scores and gender-neutral ACFT scores ( r > 0.54). However, most relationships were eliminated when partialled out by sex, which may be due to a low sample size of women. This suggests the current scoring structure utilized for men is representative of aerobic and anaerobic fitness parameters and may be able to discriminate performance levels.

Abstract Jagim, AR, Horswill, CA, Dobbs, WC, Twohey, EE, Tinsley, GM, Fields, JB, and Jones, MT. Minimum wrestling weight for high school girls wrestling: Time to revisit minimal body fat percent. J Strength Cond Res 39(3): 332–339, 2025—The purpose of this study was to determine whether an alternative body fat percentage (BF%) could be established as a safer margin for minimal wrestling weight (MWW) determination by evaluating the distribution of BF% and MWW values naturally occurring for high school girls wrestling. Data from the 2022–2023 high school season were retrospectively analyzed. In total, 33,321 female wrestlers completed skinfold (SKF) assessments or bioelectrical impedance analysis (BIA) in accordance with sport governing body mandates for weight certification. Frequency statistics and descriptive analysis were performed to compute normative MWW and BF% profiles. Body fat percentage thresholds of 12% (12MWW) and the BF% value defining the lowest fifth percentile were used to determine the resulting MWW and minimum weight class for each method. The median ± interquartile range for BF% was 28.3 ± 9.2%. There was a difference ( p < 0.001) in BF% values between BIA (28.4 ± 6.8%) and SKF (29.4 ± 7.6%), but a trivial effect size (ES = 0.14). The fifth percentile for BF% was 19%, which was used for alternative MWW determination (19MWW). 12MWW and 19MWW were 11.2 ± 6.4 kg ( p < 0.001; ES = 1.8) and 8.6 ± 7.7 kg ( p < 0.001; ES = 1.1) lower than the body mass of the wrestlers at the time of weight certification. Nearly all BF% values were above the 12% threshold currently used to determine MWW. Current body weights were more than 9.1 kg above MWW values for both 12MWW and 19MWW. Increasing the minimum BF% threshold from 12 to 19% would affect a small percentage of wrestlers and improve the margin of safety for those intent on achieving a lower weight class.

Abstract Magee, MK, Fields, JB, Jagim, A, Lockard, B, Miller, A, Stroiney, D, and Jones, MT. Estimation of whole-body bone mineral density through air displacement plethysmography in a large sample of elite athletes. J Strength Cond Res 39(4): 427–432, 2025—Dual-energy x-ray absorptiometry (DXA) is used to determine bone mineral density (BMD) and body composition. Regulations and cost may limit DXA's utility in some athletic settings. Air displacement plethysmography (ADP), while able to measure body composition, does not measure BMD. The purpose was to evaluate the influence of body composition parameters obtained from ADP on BMD. Collegiate athletes (males, n = 153; females, n = 208) underwent ADP and DXA assessments. For ADP testing, the Brozek equation was used to estimate body fat percent (BF%) and fat-free mass (FFM) from body density. Dual-energy x-ray absorptiometry tests were completed to obtain BMD using the whole-body scan mode. Stepwise regression was conducted using age, body mass, height, sex, race, FFM (ADP), BF% (ADP), and sport type as independent variables. Total BMD (DXA) was the dependent variable. Accuracy and precision of the final equation were evaluated through Bland–Altman and linear regression. The final regression equation yielded an R 2 of 0.691 with race, mass, BF%, age, and sport type as significant predictors ( p < 0.05) of BMD. Bland–Altman and linear regression showed systematic {95% confidence interval [CI] (−0.619 to −0.360)} and proportional bias (95% CI [0.173–0.374]). Although an ADP-derived regression equation may not provide a precise prediction of BMD, it may be useful to establish risk for low BMD if DXA is unavailable. Dual-energy x-ray absorptiometry may not be feasible for some athletic programs; therefore, an estimation equation for BMD derived from ADP values is advantageous for practitioners. This equation may assist in screening athletes for risk of low BMD.