The effects of training on fatigue and twitch potentiationin human skeletal muscle

Effects of 2 Types of Activation Protocols Based on Postactivation Potentiation on 50-m Freestyle Performance

Cuenca-Fernández, F, Ruiz-Teba, A, López-Contreras, G, and Arellano, R. Effects of 2 types of activation protocols based on postactivation potentiation on 50-m freestyle performance. J Strength Cond Res 34(11): 3284-3292, 2020-Postactivation potentiation (PAP) is a phenomenon which improves muscle contractility, strength, and speed in sporting performances through previously applied maximal or submaximal loads on the muscle system. This study aimed to assess the effects of 2 types of activation protocols based on PAP, on sprint swimming performance. A repeated-measures design was used to compare 3 different scenarios before a 50-m race. First, all of the participants performed a standard warm-up (SWU), consisting of a 400-m swim followed by dynamic stretching. This protocol acted as the control. Subsequently, the swimmers were randomly assigned into 2 groups: the swimmers in the first group performed the SWU followed by a PAP one-repetition maximum warm-up (RMWU), consisting of 3 "lunge" and 3 "arm stroke" repetitions, both at 85% of the one-repetition maximum. The swimmers in the second group performed the SWU followed by a PAP eccentric flywheel warm-up (EWU), consisting of one set of 4 repetitions of exercises of both the lower and upper limbs on an adapted eccentric flywheel at the maximal voluntary contraction. The time required for the swimmers to swim 5 and 10 m was shorter with the PAP protocols. The swimming velocity of the swimmers who underwent the EWU and RMWU protocols was faster at 5 and 10 m. The best total swimming time was not influenced by any of the protocols. When isolating swimming (excluding start performance and turn), best time was achieved with the SWU and RMWU compared with EWU (SWU: 20.86 ± 0.95 seconds; EWU: 21.25 ± 1.12 seconds; RMWU: 20.97 ± 1.22 seconds). In conclusion, a warm-up based on PAP protocols might exert an influence on performance in the first meters of a 50-m race. Nevertheless, other factors, such as fatigue, could modify swimming patterns and yield results contradictory to those of the desired task.

The Difference in Neuromuscular Fatigue and Workload During Competition and Training in Elite Cricketers

PURPOSE

First, to assess changes in neuromuscular function via alterations in countermovement-jump strategy after training and 2 forms of competition and second, to compare the relationship between workloads and fatigue in seam bowlers and nonseam bowlers.

METHODS

Twenty-two professional cricketers' neuromuscular function was assessed at baseline, immediately post and +24 h posttraining, and after multiday and 1-day cricket events. In addition, perceptual (rating of perceived exertion [RPE] and soreness) measures and external loads (PlayerLoad™, number of sprints, total distance, and overs) were monitored across all formats.

RESULTS

Seam bowlers covered more distance, completed more sprints, and had a higher RPE in training (P < .05), without any difference in soreness compared with nonseam bowlers. Compared with seam bowlers, the nonseam bowlers' peak force decreased post-24 h compared with baseline only in 1-d cricket (95% CI, 2.1-110.0 N; P < .04). There were no pre-post training or match differences in jump height or alterations in jump strategy (P > .05). Seam bowlers increased their peak jumping force from baseline to immediately posttraining or game (95% CI, 28.8-132.4 N; P < .01) but decreased between postcricket to +24 h (95% CI, 48.89-148.0 N; P < .001).

CONCLUSION

Seam bowlers were more accustomed to high workloads than nonseamers and thus more fatigue resistant. Changes in jump height or strategy do not appear to be effective methods of assessing fatigue in professional crickets. More common metrics such as peak force are more sensitive.

Lateral Squats Significantly Decrease Sprint Time in Collegiate Baseball Athletes

The purpose was to examine the effect of prior performance of dumbbell lateral squats (DBLS) on an agility movement-into-a-sprint (AMS) test. Twelve collegiate, resistance-trained, baseball athletes participated in three sessions separated by three days. Session One consisted of AMS baseline test, DBLS 5-RM test, and experimental protocol familiarization. Subjects were randomly assigned the protocol order for Sessions Two and Three, which consisted of warm up followed by 1-min sitting (no-DBLS) or performing the DBLS for 1 × 5 repetitions @ 5RM for each leg. Four minutes of slow recovery walking preceded the AMS test, which consisted of leading off a base and waiting for a visual stimulus. In reaction to stimulus, subjects exerted maximal effort while moving to the right by either pivoting or drop stepping and sprinting for 10 yards (yd). In Session Three, subjects switched protocols (DBLS, no-DBLS). Foot contact time (FCT), stride frequency (SF), stride length (SL), and 10-yd sprint time were measured. There were no differences between conditions for FCT, SF, or SL. Differences existed between DBLS (1.85 ± 0.09 s) and no-DBLS (1.89 ± 0.10 s) for AMS (p = 0.03). Results from the current study support the use of DBLS for performance enhancement prior to performing the AMS test.

Acute effects of extended interval training on countermovement jump and handgrip strength performance in endurance athletes: postactivation potentiation

The purpose of this study was to analyze multiple effects of an extended interval training (EIT) protocol on countermovement jump (CMJ) and handgrip strength in endurance athletes and to determine the relationship between fatigue and potentiation. Thirty experienced sub-elite male long-distance runners (age = 28.26 ± 8.27 years, body mass index = 22.24 ± 2.50 kg·m, and (Equation is included in full-text article.)= 58.7 ± 4.50 ml·kg·min) participated voluntarily in this study. Subjects performed the protocol on an outdoor running track, which consisted of 12 runs of 400 m, grouped into 4 sets of 3 runs, with a passive recovery of 1 minute between runs and 3 minutes between sets (4 × 3 × 400 m). During protocol, fatigue parameters (lactate, heart rate, and rate of perceived exertion) and performance parameters (CMJ, handgrip strength, and time spent in each 400-m run) were controlled. Analysis of variance revealed a significant improvement in CMJ (p < 0.001) throughout the protocol. Cluster analysis grouped according to whether potentiation was experienced (responders group, n = 17) or not (nonresponders group, n = 13) in relation to CMJ change from rest to fatigued condition at the end of activity. Responders group significantly improved (p ≤ 0.05) the performance in CMJ, handgrip strength and time spent in each 400-m run. Results suggest that despite induced fatigue for EIT, trained subjects can maintain their strength and power levels and their work capacity. This fact would support the rationale that improvements in performance may be due not only to metabolic adaptations but also to specific neuromuscular adaptations. Therefore, the evaluation of power should be considered simultaneously with running performance when monitoring endurance athletes.

Concurrent fatigue and potentiation in endurance athletes

PURPOSE

Countermovement jump (CMJ) and maximum running speed over a distance of 20 m were evaluated for examination of the concurrent fatigue and postactivation potentiation (PAP) in endurance athletes after an incremental field running test.

METHODS

Twenty-two endurance athletes performed two attempts of CMJ on a force plate and maximum running speed test before and following the Université de Montréal Track Test (UMTT).

RESULTS

The results showed an improvement in CMJ height (3.6%) after UMTT that correlated with the increment in peak power (3.4%), with a concurrent peak force loss (-10.8%) that correlated with peak power enhancement. The athletes maintained their 20 m sprint performance after exhaustion. Cluster analysis reinforced the association between CMJ and peak power increments in responders with a reported correlation between peak power and sprint performance increments (r = .623; P = .041); nonresponders showed an impairment of peak force, vertical stiffness, and a higher vertical displacement of the center of mass during the countermovement that correlated with lactate concentration (r = -0.717; P = .02).

CONCLUSIONS

It can be suggested that PAP could counteract the peak force loss after exhaustion, allowing the enhancement of CMJ performance and the maintenance of sprint ability in endurance athletes after the UMTT. From these results, the evaluation of CMJ after incremental running tests for the assessment of muscular adaptations in endurance athletes can be recommended.

Enhancement of jump performance after a 5-RM squat is associated with postactivation potentiation

Weight lifting exercise may induce postactivation potentiation (PAP), thereby enhancing performance of a subsequent biomechanically similar "explosive" movement. However, it has not been shown that weight lifting induces PAP, indicated as potentiation of muscle twitch force. Therefore, the present study tested whether a five repetition maximum squat (5-RM squat) both induced PAP and increased the height of subsequently performed counter-movement jumps (CMJs). Eleven male athletes completed four laboratory sessions on separate days. Two sessions determined whether the 5-RM squat induced PAP: in one, a quadriceps maximal twitch was evoked immediately before and 8 min after a set of five CMJs (control); in the other, a twitch was evoked before a CMJ set, which was followed by a 4-min rest, a 5-RM squat, a 4-min rest, and a second twitch. Another two sessions tested the effect of the 5-RM squat on jump performance: in one session, two sets of five CMJs were performed with an 8-min rest between the sets (control); in the second, a 5-RM squat was performed 4 min after the first set of CMJs, and then after another 4 min the second set of CMJs was performed. Neither twitch torque nor CMJ height changed in the control sessions (P > 0.05). In contrast, interpolation of the 5-RM squat increased (P < 0.05) both twitch torque (49.5 ± 7.8 to 54.8 ± 11.9 N m; i.e., PAP = 10.7%) and CMJ height (48.1 ± 5.6 to 49.5 ± 5.9 cm; 2.9%). Since PAP was present at the time when CMJ height increased, it was concluded that PAP may have contributed to the increased CMJ height after a 5-RM squat.

Posttetanic Potentiation in Knee Extensors after High-Frequency Submaximal Percutaneous Electrical Stimulation

Context:

The understanding of posttetanic potentiation (PTP) in human muscles induced by percutaneous electrical stimulation (PES) is important for effective application of electrical stimulation in rehabilitation.

Objective:

To examine the effect of 7-second high-frequency (100-Hz) submaximal (25% of maximal voluntary contraction force) direct PES on contractile characteristics of the knee-extensor (KE) muscles.

Design:

Single-group repeated measures.

Setting:

Kinesiology laboratory.

Subjects:

13 healthy men age 18–27 years.

Measurement:

Peak force (PF), maximal rates of force development (RFD) and relaxation (RR) of supramaximal twitch, and PF of doublet and 10-Hz tetanic contractions before and after direct tetanic PES.

Results:

A significant potentiation of twitch, doublet, and 10-Hz tetanic-contraction PF has been observed at 1–5 minutes posttetanic. Twitch RFD and RR were markedly potentiated throughout the 10-minute posttetanic period.

Conclusions:

A brief high-frequency submaximal tetanic PES induces PTP in KE muscles associated with small increase at 1–5 minutes.

Behaviour of the human gastrocnemius muscle architecture during submaximal isometric fatigue

The purpose of this study was to examine whether the human gastrocnemius medialis (GM) fascicle length and pennation angle alter during a sustained submaximal isometric plantar flexion. Fourteen male subjects performed maximal voluntary plantar flexions (MVC) on a dynamometer before and after a fatiguing task. This task consisted of a sustained submaximal isometric fatiguing contraction (40% MVC) until failure to hold the defined moment. Ultrasonography was used to visualise the muscle belly of the GM. Leg kinematics were recorded (120 Hz) to calculate the joint moment using inverse dynamics. The exerted moments and the EMG signals from GM and lateralis, soleus and tibialis anterior were measured at 1,080 Hz. The root mean square (RMS) of the EMG signal of the three triceps surae muscles increased significantly (P < or = 0.05) between 17% and 28% with fatigue. Further, the fascicle length of the GM significantly decreased from 47.1 +/- 8.0 mm at the beginning to 41.8 +/- 6.7 mm at the end of fatigue and the pennation angle increased from 23.5 +/- 4.1 degrees to 26.3 +/- 2.2 degrees (P < or = 0.05). The changes in fascicle length and pennation angle of the GM during the contraction can influence the force potential of the muscle due to the force-length relationship and the force transmission to the tendon. This provides evidence on that an additional mechanical mechanism, namely tendon creep, can contribute to the increase in the EMG activity of the GM during submaximal isometric sustained contractions.