Jacob A. Mota

Barbell Deadlift Training Increases the Rate of Torque Development and Vertical Jump Performance in Novices

Abstract Thompson, BJ, Stock, MS, Shields, JE, Luera, MJ, Munayer, IK, Mota, JA, Carrillo, EC, and Olinghouse, KD. Barbell deadlift training increases the rate of torque development and vertical jump performance in novices. J Strength Cond Res 29(1): 1–10, 2015—The primary purpose of this study was to examine the effects of 10 weeks of barbell deadlift training on rapid torque characteristics of the knee extensors and flexors. A secondary aim was to analyze the relationships between training-induced changes in rapid torque and vertical jump performance. Fifty-four subjects (age, mean ± SD = 23 ± 3 years) were randomly assigned to a control (n = 20) or training group (n = 34). Subjects in the training group performed supervised deadlift training twice per week for 10 weeks. All subjects performed isometric strength testing of the knee extensors and flexors and vertical jumps before and after the intervention. Torque-time curves were used to calculate rate of torque development (RTD) values at peak and at 50 and 200 milliseconds from torque onset. Barbell deadlift training induced significant pre- to post-increases of 18.8–49.0% for all rapid torque variables (p < 0.01). Vertical jump height increased from 46.0 ± 11.3 to 49.4 ± 11.3 cm (7.4%; p < 0.01), and these changes were positively correlated with improvements in RTD for the knee flexors (r = 0.30–0.37, p < 0.01–0.03). These findings showed that a 10-week barbell deadlift training program was effective at enhancing rapid torque capacities in both the knee extensors and flexors. Changes in rapid torque were associated with improvements in vertical jump height, suggesting a transfer of adaptations from deadlift training to an explosive, performance-based task. Professionals may use these findings when attempting to design effective, time-efficient resistance training programs to improve explosive strength capacities in novices.

Age-related reductions in muscle quality influence the relative differences in strength and power

ABSTRACT Age‐related changes in the relative differences in isokinetic strength and power may reflect fast twitch fiber function. We aimed to examine the influence of muscle quality on the relative differences in strength and power in younger and older men. Twenty younger (20.1 ± 1.5 yrs) and 20 older (69.5 ± 3.1 yrs) healthy, recreationally active men performed two plantarflexion maximal voluntary isometric contractions (MVCs) and three maximal concentric isokinetic contractions at a slow (0.52 rad·s− 1) and fast (2.09 rad·s− 1) velocity. Absolute and normalized (%MVC) isokinetic peak torque (PT), mean power (MP), peak power (PP), the relative differences in PT (%decrease), MP and PP (%increase) from 0.52 to 2.09 rad·s− 1, and electromyographic (EMG) amplitude were examined. Ultrasonography was used to determine subcutaneous fat corrected echo intensity (EI) to represent muscle quality. The younger men exhibited greater absolute isometric PT, isokinetic PT, MP, and PP at 0.52 and 2.09 rad·s− 1 (P = 0.001–0.003); but these differences were no longer present following normalization (P = 0.079–0.954). The older men exhibited similar EMG amplitude values but higher EI values (P < 0.001), a greater %decrease in PT (43.6% vs. 38.9%; P = 0.006), and a lower %increase in MP (167.5% vs. 186.3%; P = 0.049) and PP (125.5% vs. 144.5%; P = 0.006). Echo intensity was related to the %decrease in PT (r = 0.605; P < 0.001), %increase in MP (r = − 0.419; P = 0.009), and %increase in PP (r = − 0.605; P < 0.001) from 0.52 to 2.09 rad·s− 1. The absolute age‐related reductions in isokinetic strength and power were no longer present following normalization to isometric strength. However, age‐related differences in strength and power remained intact when examining the relative differences from slow to fast velocities, which appear to be influenced by the qualitative changes in skeletal muscle. HighlightsAge‐related differences in strength and power are no longer present when normalized to isometric strength.Age‐related differences remained intact when examining the relative differences from slow to fast velocities.Relative differences from slow to fast velocities are related to the qualitative changes in skeletal muscle.

Influence of Hamstring Fatigue on the Estimated Percentage of Fast-Twitch Muscle Fibers for the Vastus Lateralis.

Abstract Mota, JA, Stock, MS, Carrillo, EC, Olinghouse, KD, Drusch, AS, and Thompson, BJ. Influence of hamstring fatigue on the estimated percentage of fast-twitch muscle fibers for the vastus lateralis. J Strength Cond Res 29(12): 3509–3516, 2015—A previous study has demonstrated the ability to roughly estimate the percentage of fast-twitch muscle fibers for the vastus lateralis through the analysis of peak torque values during fatiguing isokinetic testing. We examined whether use of the hamstrings influenced peak torque and electromyographic (EMG) responses for the quadriceps during fatiguing isokinetic muscle actions. On 2 separate occasions, 21 men (mean age = 23 years) performed 50 repeated, maximal concentric isokinetic muscle actions of the left leg extensors at a velocity of 180°·s−1. For 1 trial, the subjects maximally flexed the knee joint after each full extension to bring the dynamometers lever arm back to the starting position. For the other trial, the subjects relaxed after each maximal extension and an investigator assisted in returning the lever arm. Surface EMG signals were detected from the vastus lateralis and biceps femoris throughout testing. Dependent variables that assessed the decline in peak torque and EMG mean frequency for the vastus lateralis were examined using dependent samples t-tests, effect size statistics, and the number of subjects who exceeded the minimal difference needed to be considered real. Our results showed small mean differences between the trials (Cohens d ⩽0.136). For the estimated percentage of fast-twitch fibers, none of the subjects showed a difference between trials that we considered meaningful. The mean estimated percentages of fast-twitch fibers were 61.6 and 60.1. Collectively, use of the hamstrings during fatiguing isokinetic testing of the quadriceps had little influence on peak torque and EMG.

The Influence of Habitual Protein Intake on Body Composition and Muscular Strength in Career Firefighters

ABSTRACT Objective: The aim of this research was to determine the relationship among protein (PRO) intake, body composition, and muscle strength in overweight and obese firefighters. A secondary objective was to evaluate differences in body composition and muscle strength among overweight and obese firefighters with low (L; < 0.8 g·kg−1), moderate (M; 0.8–1.0 g·kg−1), and high (H; > 1.0 g·kg−1) PRO intake. Methods: Relative PRO intake [r_PRO] was evaluated from 3-day dietary logs, self-reported by 43 overweight and obese male career firefighters (mean ± standard deviation; age = 37.3 ± 7.2 years; body mass index = 33.2 ± 5.0 kg·m−2; percent body fat [%BF] = 28.9 ± 4.0%). Body composition (fat mass [FM], %BF, lean mass [LM], percent LM [%LM]) and muscle strength (peak torque [PT], relative peak torque [r_PT] of the leg extensors) were measured using dual-energy x-ray absorptiometry and isokinetic dynamometry, respectively. Results: Greater r_PRO was associated with less FM, %BF, LM (r = −0.498 to −0.363) and greater %LM (r = 0.363), but not muscle strength (p > 0.05). Fat mass (r = −0.373) and %BF (r = −0.369) were associated with lower r_PT; %LM was associated with greater r_PT (r = 0.373). Individuals with L r_PRO had greater FM (mean difference ± standard error: L–H = 10.08 ± 3.18 kg), %BF (L–H = 3.8% ± 1.4%) and lower %LM (L–H = −3.7% ± 1.3%) than those with H r_PRO (p < 0.05) but no significant differences in muscle strength (p > 0.05). Conclusions: Protein intake > 0.8 g·kg−1 was associated with more favorable body composition in male career firefighters.

Additional insight into biarticular muscle function: The influence of hip flexor fatigue on rectus femoris activity at the knee

We evaluated the compensatory adaptations in muscle regionalization and synergist activity after fatiguing a biarticular muscle at one joint with different muscle lengths. Eleven men (mean ± SD age = 23 ± 3 years) performed 50 maximal concentric isokinetic contractions of the dominant hip flexors on two occasions. For one trial, the knee joint was fully extended. For the other, the knee joint was fixed at 70°. Maximal voluntary contractions of the knee extensors were performed immediately before and after the hip flexion fatigue protocol while bipolar surface electromyographic signals were detected from the vastus lateralis and at five points along the length of the rectus femoris. Regardless of knee joint angle during the hip flexion fatigue protocol, knee extension peak torque was unchanged following hip flexion fatigue. Electromyographic amplitude for the vastus lateralis (p = .047, η2 = .338) and rectus femoris (p < .001, η2 = .667) showed main effects for time, indicating higher and lower post-fatigue values, respectively. There was no evidence of region-specific rectus femoris adaptations during extension at the knee following fatigue of the hip flexors. These data suggest that synergistic adaptations were involved in maintaining knee extension peak torque following hip flexion fatigue.

Shifts in the relationship between motor unit recruitment thresholds versus derecruitment thresholds during fatigue

Muscle fatigue is associated with diminished twitch force amplitude. We examined changes in the motor unit recruitment versus derecruitment threshold relationship during fatigue. Nine men (mean age = 26 years) performed repeated isometric contractions at 50% maximal voluntary contraction (MVC) knee extensor force until exhaustion. Surface electromyographic signals were detected from the vastus lateralis, and were decomposed into their constituent motor unit action potential trains. Motor unit recruitment and derecruitment thresholds and firing rates at recruitment and derecruitment were evaluated at the beginning, middle, and end of the protocol. On average, 15 motor units were studied per contraction. For the initial contraction, three subjects showed greater recruitment thresholds than derecruitment thresholds for all motor units. Five subjects showed greater recruitment thresholds than derecruitment thresholds for only low-threshold motor units at the beginning, with a mean cross-over of 31.6% MVC. As the muscle fatigued, many motor units were derecruited at progressively higher forces. In turn, decreased slopes and increased y-intercepts were observed. These shifts were complemented by increased firing rates at derecruitment relative to recruitment. As the vastus lateralis fatigued, the central nervous systems compensatory adjustments resulted in a shift of the regression line of the recruitment versus derecruitment threshold relationship.

Adaptations associated with an after-school strength and conditioning program in middle-school aged boys: A quasi-experimental design

Abstract Thompson, BJ, Stock, MS, Mota, JA, Drusch, AS, DeFranco, RN, Cook, TR, and Hamm, MA. Adaptations associated with an after-school strength and conditioning program in middle-school aged boys: a quasi-experimental design. J Strength Cond Res 31(10): 2840–2851, 2017—High-intensity strength and conditioning programs aimed at improving youth performance are becoming increasingly prevalent. The purpose of this study was to investigate the effects of a 16-week after-school strength and conditioning program on performance and body composition in middle-school-aged boys. Subjects in the training group (n = 16, mean age = 11.8 years) performed 90 minutes of supervised plyometric and resistance training twice weekly for 16 weeks. A group of control subjects (n = 9, age = 12.1 years) maintained their current activity levels. Sprint speed, 5-10-5 proagility, jump height, isometric peak torque of the leg extensors and flexors, and dual energy x-ray absorptiometry-derived body composition were examined during pretesting and posttesting. Data were analyzed by performing independent samples t-tests on the absolute change scores between groups. The primary findings were that the training intervention elicited significant improvements in 20-m sprint times (p = 0.03; mean change for training group = −0.17 seconds) and body-fat percentage (p = 0.03; 2.5% absolute improvement), the latter of which was a function of reduced fat mass (p = 0.06; −0.84 kg). Between-group differences were not noted for agility, jump height, lean mass, or strength measures; however, effect sizes generally showed greater improvements for the training group. In contrast to findings in longitudinal studies performed in collegiate athletes, sprint speed may be particularly adaptable during adolescence. In addition to potentially improving sport performance, high-intensity plyometric and resistance training programs offer the added benefit of improved body composition. These programs appear less effective for agility and jump performance and do not elicit substantial improvements in muscle mass above maturation.