Elastic band exercise induces greater neuromuscular fatigue than phasic isometric contractions

Postactivation Performance Enhancement of Amateur Boxers’ Punch Force and Neuromuscular Performance Following 2 Upper-Body Conditioning Activities

Purpose: The purpose of this study was to assess the efficacy of upper-body punch-specific isometric (ISO) and elastic resistance (ER) conditioning activities (CAs) on the punch force and neuromuscular performance of amateur boxers. Methods: Ten male senior elite amateur boxers (19.7 [1.2]| y; height 180.9 [7.0] cm; mass 78.7 [9.6] kg) visited the laboratory on 4 separate occasions. Initially, the participants performed baseline physical tests comprising bench-press 1-repetition maximum and countermovement jumps. On the other 3 occasions, the boxers performed maximal punches against a vertically mounted force plate and maximal countermovement jumps prior to and following an ISO or ER CA, as well as a control trial. Results: No interactions between CA × time were found in all performance variables. As observed by mean changes, effect sizes, and signal:noise ratio, both the ISO and ER, but not the control trial, consistently produced small to moderate, worthwhile increases in punch force and rate of force development, with the greatest increases in performance typically observed in the ISO trial. No meaningful improvements were observed in countermovement jump performance in all trials, indicative of a localized postactivation performance enhancement effect. Conclusion: In conclusion, the ISO and ER CAs may be implemented in an amateur boxers’ warm-up to acutely enhance punch-force variables, although the ISO punch appears to be the superior CA to improve punch-specific performance. The CAs used in the present study may also be relevant to other combat sports inclusive of a striking element.

The Effects of Verbal Instructions on Lower Limb Muscles' Excitation in Back-Squat

The present study investigated whether or not verbal instruction affects the electromyographic (EMG) amplitude of back-squat prime movers. Fifteen resistance-trained men performed back-squat at 50%1-RM and 80%1-RM and received external (EF) or internal focus (IF) on lower-limb posterior muscles. EMG amplitude of gluteus maximus, biceps femoris, gastrocnemius medialis, vastus lateralis, and tibialis anterior was recorded during both concentric and eccentric phases. During the concentric phase, the gluteus maximus and biceps femoris EMG amplitude was greater in IF vs EF at 50% [effect size (ES): 0.63 (95%CI 0.09/1.17) and 0.49 (0.10/0.78), respectively] and 80% [ES: 1.30 (0.29/2.21) and 0.59 (0.08/1.10)]. The gastrocnemius medialis EMG amplitude was greater in IF vs EF during the eccentric phase at 50% [ES: 0.73 (0.13/1.33)] and at 80% [ES: 0.72 (0.10/1.34)]. Concomitantly, vastus lateralis EMG amplitude was lower at 50% [ES: -0.71 (-1.38/-0.04)] and 80% [ES: -0.68 (-1.33/-0.03)]. During the eccentric phase, the tibialis anterior EMG amplitude was greater in IF vs EF at 50% [ES: 0.90 (0.12 to 1.68)] and 80% [ES: 0.74 (0.13/1.45)]. Irrespective of the load, in the thigh muscles the internal focus promoted a different motor pattern, increasing the hip extensors and reducing the knee extensor excitation during the concentric phase. Concomitantly, both ankle muscles were more excited during the eccentric phase, possibly to increase the anterior-posterior balance control. The internal focus in back-squat seems to have phase-dependent effects, and it is visible at both moderate and high loads.

Neuromuscular Correlates of the Contralateral Stretch-induced Strength Loss

PURPOSE

The current study investigated the effects of unilateral passive stretching on the neuromuscular mechanisms involved in the force-generating capacity of the contralateral muscle.

METHODS

Twenty-six healthy men underwent unilateral passive stretching of the plantarflexors (5 × 45 s on + 15 s off; total stretching time, 225 s). Before and after the stretching protocol, contralateral ankle range of motion, maximum voluntary contraction (MVC) of the plantarflexors, and surface electromyographic root-mean-square (sEMG RMS) of the soleus and the gastrocnemii muscles were determined. Concurrently, V-wave, maximum and superimposed H-reflex, and M-wave were elicited via nerve stimulation to estimate the supraspinal, spinal, and peripheral mechanisms, respectively. sEMG RMS, V-wave, and H-reflex were normalized to the M-wave.

RESULTS

After passive stretching, contralateral ankle range of motion was increased (+8% [1%/15%], effect size [ES] = 0.43 [0.02/0.84], P < 0.001), MVC of the plantarflexors was decreased (-9% [-21%/-2%], ES = -0.96 [-1.53/-0.38], P < 0.001), and the sEMG RMS/M-wave of the soleus and the gastrocnemii muscles was decreased (≈-9%, ES ≈ -0.33, P < 0.05). Concurrently, the V-wave/M-wave superimposed was decreased in all muscles (≈-13%, ES = -0.81 to -0.52, P < 0.05). No change in H-reflex/M-wave and M-wave was observed under both maximum and superimposed condition. The decrease in the MVC and the sEMG RMS of the contralateral muscle was accompanied by a decrease in the V-wave/M-wave but not the H-reflex/M-wave ratios and the M-wave.

CONCLUSIONS

The present outcomes suggest that only supraspinal mechanisms might be involved in the contralateral decrease in the maximum force-generating capacity.

No effect of passive stretching on neuromuscular function and maximum force-generating capacity in the antagonist muscle

Purpose

The present study investigated whether or not passive stretching increases the force-generating capacity of the antagonist muscle, and the possible neuromuscular mechanisms behind.

Methods

To this purpose, the neuromuscular function accompanying the force-generating capacity was assessed in 26 healthy male volunteers after passive stretching and in a control session. Before and after passive intermittent static stretching of the plantar flexors consisting of five sets × 45 s + 15 s-rest, maximum voluntary isometric contraction (MVC) and surface electromyographic root mean square (sEMG RMS) were measured in the tibialis anterior (the antagonist muscle). Additionally, evoked V wave, H-reflex, and M wave were elicited by nerve stimulation at rest and during MVC. Ankle range of motion (ROM) and plantar flexors MVC and EMG RMS were measured to check for the effectiveness of the stretching manoeuvre.

Results

No change in MVC [p = 0.670; effect size (ES) − 0.03] and sEMG RMS/M wave during MVC (p = 0.231; ES − 0.09) was observed in the antagonist muscle after passive stretching. Similarly, no change in V wave (p = 0.531; ES 0.16), H-reflex at rest and during MVC (p = 0.656 and 0.597; ES 0.11 and 0.23, respectively) and M wave at rest and during MVC (p = 0.355 and 0.554; ES 0.04 and 0.01, respectively) was observed. An increase in ankle ROM (p < 0.001; ES 0.55) and a decrease in plantar flexors MVC (p < 0.001; ES − 1.05) and EMG RMS (p < 0.05; ES − 1.72 to − 0.13 in all muscles) indicated the effectiveness of stretching protocol.

Conclusion

No change in the force-generating capacity and neuromuscular function of the antagonist muscle after passive stretching was observed.

Design and Validation of Multichannel Wireless Wearable SEMG System for Real-Time Training Performance Monitoring

Monitoring of training performance and physical activity has become indispensable these days for athletes. Wireless technologies have started to be widely used in the monitoring of muscle activation, in the sport performance of athletes, and in the examination of training efficiency. The monitorability of performance simultaneously in the process of training is especially a necessity for athletes at the beginner level to carry out healthy training in sports like weightlifting and bodybuilding. For this purpose, a new system consisting of 4 channel wireless wearable SEMG circuit and analysis software has been proposed to detect dynamic muscle contractions and to be used in real-time training performance monitoring and analysis. The analysis software, the Haar wavelet filter with threshold cutting, can provide performance analysis by using the methods of moving RMS and %MVC. The validity of the data obtained from the system was investigated and compared with a biomedical system. In this comparison, 90.95% ± 3.35 for left biceps brachii (BB) and 90.75% ± 3.75 for right BB were obtained. The output of the power and %MVC analysis of the system was tested during the training of the participants at the gym, and the training efficiency was measured as 96.87% ± 2.74.