Effects of Plyometric and Resistance Training on Muscle Strength, Explosiveness, and Neuromuscular Function in Young Adolescent Soccer Players.

McKinlay, BJ, Wallace, P, Dotan, R, Long, D, Tokuno, C, Gabriel, D, and Falk, B. Effects of plyometric and resistance training on muscle strength, explosiveness, and neuromuscular function in young adolescent soccer players. J Strength Cond Res 32(11): 3039-3050, 2018-This study examined the effect of 8 weeks of free-weight resistance training (RT) and plyometric (PLYO) training on maximal strength, explosiveness, and jump performance compared with no added training (CON), in young male soccer players. Forty-one 11- to 13-year-old soccer players were divided into 3 groups (RT, PLYO, and CON). All participants completed isometric and dynamic (240°·s) knee extensions before and after training. Peak torque (pT), peak rate of torque development (pRTD), electromechanical delay (EMD), rate of muscle activation (Q50), m. vastus lateralis thickness (VLT), and jump performance were examined. Peak torque, pRTD, and jump performance significantly improved in both training groups. Training resulted in significant (p ≤ 0.05) increases in isometric pT (23.4 vs. 15.8%) and pRTD (15.0 vs. 17.6%), in RT and PLYO, respectively. During dynamic contractions, training resulted in significant increases in pT (12.4 and 10.8% in RT and PLYO, respectively), but not in pRTD. Jump performance increased in both training groups (RT = 10.0% and PLYO = 16.2%), with only PLYO significantly different from CON. Training resulted in significant increases in VLT (RT = 6.7% and PLYO = 8.1%). There were no significant EMD changes. In conclusion, 8-week free-weight resistance and plyometric training resulted in significant improvements in muscle strength and jump performance. Training resulted in similar muscle hypertrophy in the 2 training modes, with no clear differences in muscle performance. Plyometric training was more effective in improving jump performance, whereas free-weight RT was more advantageous in improving peak torque, where the stretch reflex was not involved.

Isometric and dynamic strength and neuromuscular attributes as predictors of vertical jump performance in 11- to 13-year-old male athletes.

In explosive contractions, neural activation is a major factor in determining the rate of torque development, while the latter is an important determinant of jump performance. However, the contribution of neuromuscular activation and rate of torque development to jump performance in children and youth is unclear. The purpose of this study was to examine the relationships between the rate of neuromuscular activation, peak torque, rate of torque development, and jump performance in young male athletes. Forty-one 12.5 ± 0.5-year-old male soccer players completed explosive, unilateral isometric and dynamic (240°/s) knee extensions (Biodex System III), as well as countermovement-, squat-, and drop-jumps. Peak torque (pT), peak rate of torque development (pRTD), and rate of vastus lateralis activation (Q30) during the isometric and dynamic contractions were examined in relation to attained jump heights. Isometric pT and pRTD were strongly correlated (r = 0.71) but not related to jump performance. Dynamic pT and pRTD, normalized to body mass, were significantly related to jump height in all 3 jumps (r = 0.38-0.66, p < 0.05). Dynamic normalized, but not absolute pRTD, was significantly related to Q30 (r = 0.35, p < 0.05). In young soccer players, neuromuscular activation and rate of torque development in dynamic contractions are related to jump performance, while isometric contractions are not. These findings have implications in the choice of training and assessment methods for young athletes.

The Electromyographic Threshold in Girls and Women.

BACKGROUND: The electromyographic threshold (EMGTh) is thought to reflect increased high-threshold/type-II motor-unit (MU) recruitment and was shown higher in boys than in men. Women differ from men in muscular function. PURPOSE: Establish whether females' EMGTh and girls-women differences are different than males'. METHODS: Nineteen women (22.9 ± 3.3yrs) and 20 girls (10.3 ± 1.1yrs) had surface EMG recorded from the right and left vastus lateralis muscles during ramped cycle-ergometry to exhaustion. EMG root-mean-squares were averaged per pedal revolution. EMGTh was determined as the least residual sum of squares for any two regression-line data divisions, if the trace rose ≥ 3SD above its regression line. EMGTh was expressed as % final power-output (%Pmax) and %VO2pk power (%PVO2pk). RESULTS: EMGTh was detected in 13 (68%) of women, but only 9 (45%) of girls (p < .005) and tended to be higher in the girls (%Pmax= 88.6 ± 7.0 vs. 83.0 ± 6.9%, p = .080; %PVO2pk= (101.6 ± 17.6 vs. 90.6 ± 7.8%, p = .063). When EMGTh was undetected it was assumed to occur at 100%Pmax or beyond. Consequently, EMGTh values turned significantly higher in girls than in women (94.8 ± 7.4 vs. 88.4 ± 9.9%Pmax, p = .026; and 103.2 ± 11.7 vs. 95.2 ± 9.9%PVO2pk, p = .028). CONCLUSIONS: During progressive exercise, girls appear to rely less on higher-threshold/type-II MUs than do women, suggesting differential muscle activation strategy.

The electromyographic threshold in boys and men.

BACKGROUND: Children have been shown to have higher lactate (LaTh) and ventilatory (VeTh) thresholds than adults, which might be explained by lower levels of type-II motor-unit (MU) recruitment. However, the electromyographic threshold (EMGTh), regarded as indicating the onset of accelerated type-II MU recruitment, has been investigated only in adults. PURPOSE: To compare the relative exercise intensity at which the EMGTh occurs in boys versus men. METHODS: Participants were 21 men (23.4 ± 4.1 years) and 23 boys (11.1 ± 1.1 years), with similar habitual physical activity and peak oxygen consumption (VO2pk) (49.7 ± 5.5 vs. 50.1 ± 7.4 ml kg(-1) min(-1), respectively). Ramped cycle ergometry was conducted to volitional exhaustion with surface EMG recorded from the right and left vastus lateralis muscles throughout the test (~10 min). The composite right-left EMG root mean square (EMGRMS) was then calculated per pedal revolution. The EMGTh was then determined as the exercise intensity at the point of least residual sum of squares for any two regression line divisions of the EMGRMS plot. RESULTS: EMGTh was detected in 20/21 of the men (95.2 %) and only in 18/23 of the boys (78.3 %). The boys' EMGTh was significantly higher than the men's (86.4 ± 9.6 vs. 79.7 ± 10.0 % of peak power output at exhaustion; p < 0.05). The pattern was similar when EMGTh was expressed as percentage of VO2pk. CONCLUSIONS: The boys' higher EMGTh suggests delayed and hence lesser utilization of type-II MUs in progressive exercise, compared with men. The boys-men EMGTh differences were of similar magnitude as those shown for LaTh and VeTh, further suggesting a common underlying factor.