Comparison of fatigue responses and rapid force characteristics between explosive- and traditional-resistance-trained males.

PURPOSE: To compare maximal and rapid force characteristics, as well as fatigability, between traditional (TRT) and explosive (ERT) resistance-trained men. METHODS: Fourteen TRT (mean age = 25 years) and twelve ERT (mean age = 22 years) men performed rapid maximal contractions followed by an isokinetic fatigue protocol consisting of 50 maximal knee extension (KE) and flexions (KF) at a moderate speed (180° s-¹). Baseline measures included: isokinetic peak torque (PT), isometric rate of torque development (RTD0-50), peak acceleration (ACCmax), and peak velocity (Vmax). Changes in torque with fatigue were used to calculate a fatigue index (FI%). RESULTS: The ERT group (M ± SD; 1199.05 ± 404.12) displayed a significantly higher isometric RTD0-50 (p = 0.049) during KE than the TRT group (931.73 ± 244.75). No other significant differences in the dependent variables (PT, FI%, ACCmax, Vmax; all p ≥ 0.05) were observed between groups (TRT vs. ERT) for either of the muscle groups (KE and KF). CONCLUSIONS: The results of the present study indicated that only knee extension RTD was able to discriminate between the two groups. These findings suggest that rapid force production may be more sensitive at distinguishing training-specific muscular adaptations than peak acceleration or velocity.

Physical Performance Among Air Force ROTC Cadets Following Non-Mandatory Training.

INTRODUCTION: Due to the standard collegiate academic calendar (two semesters), U.S. Air Force Reserve Officers Training Corps (ROTC) cadets have an approximate 3-mo break over the summer in which physical training (PT) is neither regulated nor required. The purpose of this investigation was to determine if significant changes in cadet physical fitness assessment (PFA) scores occur after a 3-mo summer break when training is not mandatory.METHODS: Male (N 28) and female (N 10) cadets performed the PFA in April and August. Cadets were split into two groups depending on if they participated in field training over the summer [FT; N 12 (men 6, women 6)] or did not [NFT; N 26 (men 22, women 4)] to determine if engaging in field training had any effect on performance.RESULTS: Cadets performed significantly better on run time (7%), pushups (7.6%), sit-ups (5.8%), and overall composite score (3.6%) before summer break compared to after. Significant time group interactions were observed for abdominal circumference and run time. Abdominal circumference paired samples t-tests indicated that while the FT group did not differ between the spring and fall time points, the NFT did. There was a main effect for time in which cadets had a significantly larger abdominal circumference in the spring compared to the fall semester.CONCLUSION: Nonmandatory physical training over summer break may significantly decrease a cadets performance on the PFA. Additionally, it appears that even the inclusion of field training for some cadets was not enough to prevent the detraining that took place over summer break.Mackey CS, Johnson Q, Dawes JJ, DeFreitas JM. Physical performance among Air Force ROTC cadets following non-mandatory training. Aerosp Med Hum Perform. 2020; 91(10):818823.

Effects of Power-Endurance and Controlled Heavy Squat Protocols on Vertical Jump Performance in Females.

The purpose of this investigation was to examine the immediate and acute vertical jump performance responses throughout and following two different free-weight back squat exercise protocols. Fifteen resistance-trained women (mean ± SD: age = 21.8 ± 0.9 years; height = 164.6 ± 8.4 cm; mass = 68.5 ± 9.2 kg) performed vertical jumps before (Pre), immediately after each set (S1-S5), and up to 20 minutes post squat exercise (Post0-Post20) of either a power-endurance (PE; 5×16 at 40% 1-RM) or controlled heavy (CHP; 5×8 at 80%) protocol. Participants' jump height (JH), mean (MP), peak power (PP), mean (MV) and peak velocity (PV) were measured using a linear position transducer. 2-way repeated measures ANOVAs were run for all dependent variables. In the case of the violation of sphericity Greenhouse-Geisser results were reported. No significant intensity × time interactions were observed for any of the variables (p = 0.30-0.87). Main effects for time were observed (p ≤ 0.001, ηp2 = 0.52) for MP and MV, which were significantly lower than Pre at S2 through S5-Post0 (p = 0.001-0.02) time points. Additionally, main effects for time were observed (p ≤ 0.001, ηp2 = 0.43) for PP and PV, which were significantly lower than Pre at all time points (p = 0.001-0.03) with the exception of Post10 (p = 0.17-0.21). Lastly, JH was significantly lower than Pre for all time points (p ≤ 0.001-0.02) except for Post5 (p = 0.13) and Post10 (p = 0.25). This study suggests overall training volume and not training-load could have attributed to the similar fatigue and recovery-related responses that were observed. The present findings suggest that vertical jump performance may be negatively affected following moderate to heavy exercise for up to 20 minutes.

A longitudinal analysis of the U.S. Air Force reserve officers' training corps physical fitness assessment.

BACKGROUND: The U.S. Air Force physical fitness assessment (PFA) is used to determine the overall fitness of their personnel. It is currently unknown to what extent the PFA scores of Reserve Officers' Training Corps (ROTC) cadets are affected by mandatory physical training. The purpose of this investigation was to longitudinally examine the PFAs of ROTC cadets over a four-year period, evaluate the results across class ranks, and evaluate the sensitivity of the classification of the tests. METHODS: Air Force ROTC cadets performed the PFAs (abdominal circumference, 1-min pushups, 1-min sit-ups, and a 1.5-mile run) in both the spring (n = 26) and fall (n = 22) semesters. PFAs were compiled over a four-year period (Spring 2014 - Fall 2017) and were performed in accordance with Air Force Instruction 36-2905. A one-way repeated measures ANOVA was performed separately for the fall and spring groups for each dependent variable across the 4 years. Additionally, a one-way between groups ANOVA was performed for each dependent variable during the time point (fall 2015; N = 46) with the most recorded cadets for each class rank. RESULTS: Longitudinal assessments revealed a main effect of time (P = 0.010) on abdominal circumference; cadets had a smaller abdominal circumference in their freshman year than in their senior year. A main effect of time (P = 0.006) was also observed on sit-up quantity; cadets performed more sit-ups in their junior year than in their freshman year. Examining between class ranks during the same year (between-subjects ANOVA) revealed a main effect of class rank on sit-up quantity (P = 0.003); the freshmen completed fewer repetitions than the sophomores (P = 0.018) and the juniors did (P = 0.001). CONCLUSION: The results indicated that only the sit-up component showed differences between class ranks. These findings suggest that the Air Force PFA may not be sensitive enough to detect changes in physical fitness or distinguish between class ranks regarding physical performance, even after years of training. This limitation may be in part due to the limited duration of training incorporated by the ROTC program (2 h per week), which provided a maintenance effect rather than improvement in physical performance. We recommend that more attention be directed to the efficacy of physical training, the sensitivity of measures included in the PFA, or both.

Body Composition Comparison of Upper- and Underclass Reserve Officers' Training Corps Cadets.

INTRODUCTION: Body composition (BC) measurements are used to determine qualification for enlistment and to ensure active members are meeting standards. Although there is extensive research on BC in active-duty military, very few have examined ROTC cadets. The purpose of this study was to identify and quantify differences in BC between freshman/sophomore [underclass (UND)] and junior/senior [upperclass (UPP)] ROTC cadets by using bioelectrical impedance spectroscopy (BIS).METHODS: UND (N = 21) and UPP (N = 15) Air Force ROTC cadets volunteered for this study. BIS was used to measure fat mass percentage (FM%), fat free mass percentage (FFM%), total body water percentage (TBW%), extracellular fluid percentage (ECF%), and intracellular fluid percentage (ICF%). Separate one-way ANOVAs were run between UND and UPP for all dependent variables with a Bonferroni correction factor. Additionally, a Pearson correlation between abdominal circumference (AC) and FM% was conducted.RESULTS: No significant differences were observed between the UND and UPP groups' BMI. However, significant differences were observed for ECF%, ICF%, TBW%, FFM%, and FM% in which the UPP had a higher TBW%, ICF%, FFM%, and a lower ECF% and FM% compared to the UND.CONCLUSIONS: This study observed significant differences in BC across class ranks in ROTC cadets. Findings from this study suggest that due to an increased exposure to ROTC training, UPP cadets have a more ideal body composition (FFM% and FM%) when compared to UND cadets.Johnson QR, Mackey CS, Muddle TD, Smith DB, DeFreitas JM. Body composition comparison of upper- and underclass Reserve Officers Training Corps cadets. Aerosp Med Hum Perform. 2019; 90(9):813-818.

Muscle phenotype is related to motor unit behavior of the vastus lateralis during maximal isometric contractions.

Previous investigations have reported a relationship between skeletal muscle phenotype and motor unit (MU) firing parameters during submaximal contractions. The purpose of the current investigation, however, was to examine the relationships between motor unit firing behavior during a maximal voluntary contraction, Myosin Heavy Chain (MHC) isoform content, and various molecular neuromuscular targets of the vastus lateralis (VL) muscle in resistance-trained men. Ten resistance-trained males completed a trapezoidal ramp contraction up to 100% of their maximal voluntary isometric strength (MVIC). Surface electromyography was recorded from the VL using a multichannel electrode array and decomposed to examine the firing characteristics of individual MUs. A skeletal muscle biopsy of the VL was also collected from each subject. Regression analyses were performed to identify relationships between type II fiber area and the slopes and/or intercepts of the mean firing rate (FRMEAN ) versus recruitment threshold (RT), max firing rate (FRMAX ) versus RT, and RT versus MU action potential amplitude (MUAPPP ) relationships. There were significant inverse relationships between type II fiber area and the y-intercept of the FR versus RT relationship (P < 0.05). Additionally, strong relationships (r > 0.5) were found between type II fiber area and FRMEAN versus RT slope and RT versus MUAPPP slope and intercept. These data further support the hypothesis that skeletal muscle phenotype is related to MU behavior during isometric contraction. However, our data, in concert with previous investigations, may suggest that these relationships are influenced by the intensity of the contraction.

Effects of a pre-workout supplement on hyperemia following leg extension resistance exercise to failure with different resistance loads.

BACKGROUND: We sought to determine if a pre-workout supplement (PWS), containing multiple ingredients thought to enhance blood flow, increases hyperemia associated with resistance training compared to placebo (PBO). Given the potential interaction with training loads/time-under-tension, we evaluated the hyperemic response at two different loads to failure. METHODS: Thirty males participated in this double-blinded study. At visit 1, participants were randomly assigned to consume PWS (Reckless™) or PBO (maltodextrin and glycine) and performed four sets of leg extensions to failure at 30% or 80% of their 1-RM 45-min thereafter. 1-wk. later (visit 2), participants consumed the same supplement as before, but exercised at the alternate load. Heart rate (HR), blood pressure (BP), femoral artery blood flow, and plasma nitrate/nitrite (NOx) were assessed at baseline (BL), 45-min post-PWS/PBO consumption (PRE), and 5-min following the last set of leg extensions (POST). Vastus lateralis near infrared spectroscopy (NIRS) was employed during leg extension exercise. Repeated measures ANOVAs were performed with time, supplement, and load as independent variables and Bonferroni correction applied for multiple post-hoc comparisons. Data are reported as mean ± SD. RESULTS: With the 30% training load compared to 80%, significantly more repetitions were performed (p < 0.05), but there was no difference in total volume load (p > 0.05). NIRS derived minimum oxygenated hemoglobin (O2Hb) was lower in the 80% load condition compared to 30% for all rest intervals between sets of exercise (p < 0.0167). HR and BP did not vary as a function of supplement or load. Femoral artery blood flow at POST was higher independent of exercise load and treatment. However, a time*supplement*load interaction was observed revealing greater femoral artery blood flow with PWS compared to PBO at POST in the 80% (+56.8%; p = 0.006) but not 30% load condition (+12.7%; p = 0.476). Plasma NOx was ~3-fold higher with PWS compared to PBO at PRE and POST (p < 0.001). CONCLUSIONS: Compared to PBO, the PWS consumed herein augmented hyperemia following multiple sets to failure at 80% of 1-RM, but not 30%. This specificity may be a product of interaction with local perturbations (e.g., reduced tissue oxygenation levels [minimum O2Hb] in the 80% load condition) and/or muscle fiber recruitment.

Molecular, neuromuscular, and recovery responses to light versus heavy resistance exercise in young men.

Recent evidence suggests that resistance training with light or heavy loads to failure results in similar adaptations. Herein, we compared how both training modalities affect the molecular, neuromuscular, and recovery responses following exercise. Resistance-trained males (mean ± SE: 22 ± 2 years, 84.8 ± 9.0 kg, 1.79 ± 0.06 m; n = 15) performed a crossover design of four sets of leg extensor exercise at 30% (light RE) or 80% (heavy RE) one repetition maximum (1RM) to repetition failure, and heavy RE or light RE 1 week later. Surface electromyography (EMG) was monitored during exercise, and vastus lateralis muscle biopsies were collected at baseline (PRE), 15 min (15mPOST), and 90 min following RE (90mPOST) for examination of molecular targets and fiber typing. Isokinetic dynamometry was also performed before (PRE), immediately after (POST), and 48 h after (48hPOST) exercise. Dependent variables were analyzed using repeated measures ANOVAs and significance was set at P ≤ 0.05. Repetitions completed were greater during light RE (P < 0.01), while EMG amplitude was greater during heavy RE (P ≤ 0.01). POST isokinetic torque was reduced following light versus heavy RE (P < 0.05). Postexercise expression of mRNAs and phosphoproteins associated with muscle hypertrophy were similar between load conditions. Additionally, p70s6k (Thr389) phosphorylation and fast-twitch fiber proportion exhibited a strong relationship after both light and heavy RE (r > 0.5). While similar mRNA and phosphoprotein responses to both modalities occurred, we posit that heavy RE is a more time-efficient training method given the differences in total repetitions completed, lower EMG amplitude during light RE, and impaired recovery response after light RE.