What are the best isometric exercises of muscle potentiation?

Postsubmaximal Isometric Full Squat Jump Potentiation in Trained Men

ABSTRACT

Koźlenia, D, and Domaradzki, J. Postsubmaximal isometric full squat jump potentiation in trained men. J Strength Cond Res 38(3): 459-464, 2024-This study investigated the effects of postsubmaximal isometric full squats on jump height (JH). The study included 45 men aged 20-27 years with at least 6 years of resistance training experience that had been continuous for at least 2 years and a minimum relative strength of 120% of body mass in the full-back squat. They were randomly divided into an experimental group (EG) and a control group (CG). After a standard warm-up, subjects performed a countermovement jump (CMJ) to ascertain a baseline value. A conditioning activity (CA) introduced in the EG involved three 4-second sets of a high bar isometric full-back squat at 70% repetition maximum, with a 1-minute break. Five CMJs were performed in the following 9 minutes. Statistical significance was set at α = 0.05. A 2-way analysis of covariance (ANCOVA) (group-time), with baseline CMJ as a covariable, revealed statistically significant differences between groups ( p < 0.0001). The Bonferroni post hoc tests revealed higher results in the EG at the third, fifth, seventh, and ninth minutes ( p < 0.05). A 1-way repeated-measures analysis of variance (ANOVA) showed that time was statistically significant within groups ( p < 0.0001). The post hoc tests indicated JH improvement after 3 minutes compared with the baseline, and the trend persisted in the following 6 minutes ( p < 0.05) in the EG. The postactivation performance enhancement (PAPE) protocol based on a submaximal isometric full squat enhanced JH in the third minute after CA, which persisted for at least 6 minutes. These results indicate a requirement to evoke performance enhancement in response to an isometric CA.

The effectiveness of isometric protocols using an external load or voluntary effort on jump height enhancement in trained females

This study aimed to examine the effectiveness of isometric post-activation performance enhancement protocols using an external load (EXL) or voluntary effort (VE) on jump height (JH) in trained females divided into EXL (n = 15), VE (n = 14), and control (CON; n = 12) groups. JH was assessed using countermovement jumps at baseline and the third, fifth, seventh, and ninth minutes after the protocols. The EXL performed three sets of back squats with a 70%-repetition maximum load for four seconds, with one-minute breaks. The VE performed three sets of pushing against an immovable bar in the back squat position for five seconds, with one-minute breaks. The CON group ran on a treadmill at 6 km/h for four minutes. A RM-ANOVA showed a significant interaction for group-time (p < 0.01). The EXL protocol provided JH improvement at the third minute compared to baseline (p = 0.01), though it decreased in subsequent minutes (p < 0.05). JH declined in the VE group at the third and fifth minutes (p < 0.05), then peaked, surpassing baseline, after nine minutes (p = 0.04). No significant differences were found between the protocols in the relative effect (best-baseline) (p = 0.09), though the EXL group appeared to gain more (effect size [ES] = 0.76). Both protocols improved JH, but caution is required due to peak performance time and potential JH reduction.

Post-Activation Performance Enhancement as a Strategy to Improve Bench Press Performance to Volitional Failure

Post-Activation Performance Enhancement (PAPE) has been commonly used as a strategy to improve acute force production, although its effects on performance to volitional failure are still unknown. The aim of this study was to analyse the influence of a PAPE protocol on bench press performance in a training set to volitional failure in trained individuals. Fourteen participants with at least two years of resistance training experience (age 24.57 ± 2.7 years; body mass 77.47 ± 12.2 kg; body height 174.21 ± 7.4 cm; medium grip bench press 1 repetition maximum (1RM): 101.6 ± 25.8 kg), of which 14 completed the control protocol and 12 completed the experimental protocol, took part in the study. After a standardised warm-up, participants completed three sessions: 1) a 1RM test for the medium grip bench press, 2) a control condition consisting of a set of the bench press to volitional failure with 80% 1RM (CON), and 3) an experimental condition consisting of a set of the bench press to volitional failure with 80% 1RM after a PAPE protocol (PAPE). The PAPE protocol consisted of a heavy set of one repetition with their 93% 1RM as the conditioning activity. Under the PAPE condition, participants performed significantly more repetitions than under the CON condition (p = 0.008, ES = 0.5, small effect), their last repetition was slower (p = 0.02, ES = 0.52, small effect) and presented a higher velocity loss (p = 0.004, ES = 0.75, moderate effect). These results suggest that a traditional PAPE protocol improves the number of repetitions performed to volitional failure.

Intermittent Voluntary Isometric Contractions Effects on Performance Enhancement and Sticking Region Kinematics in the Bench Press

During the last years, post-activation performance enhancement (PAPE) has gained notorious popularity due to the capacity to improve the acute rate of force development (RFD) using different strategies with different muscle contraction regimes as conditioning stimuli. The aim of the present study was to analyse the role of a maximal isometric post-activation performance enhancement (PAPE) protocol in performance and its effects on the kinematics of the sticking region. Twenty-one trained participants (age 26.4 ± 5.4 years) underwent two experimental sessions: an experimental session consisting of a single set and a single repetition of the bench press at the 93% of 1RM (which is considered a traditional conditioning activity to induce PAPE) (TRAD) and an isometric experimental session (ISO) consisting of 15 maximal voluntary isometric contractions in the sticking region of the medium grip bench press lasting 1 s with a 1 s rest interval between contractions. Both TRAD and ISO experimental conditions improved performance from post0 to post4, post8, post12 and post16, but only the ISO condition improved performance from the start of the lift to the start of the sticking region from pre to post (p < 0.001), and only the ISO condition improved maximum (p = 0.005) and minimum (p = 0.025) peak velocities. The results of this study suggest that short duration maximal voluntary isometric contractions improve the velocity of the lift prior to the initiation of the sticking region, which ultimately improves the impulse and facilitates the lift.

Joint-specific Postactivation Potentiation Enhances Serve Velocity in Young Tennis Players

ABSTRACT

Baiget, E, Colomar, J, and Corbi, F. Joint-specific postactivation potentiation enhances serve velocity in young tennis players. J Strength Cond Res 37(4): 840-847, 2023-This study aimed (a) to analyze the influence of sport-specific postactivation potentiation (PAP) on serve velocity (SV) and serve accuracy (SA) in young tennis players, (b) to compare the PAP effects of 2 different conditioning activities (CA) on SV and SA, and (c) to explore if changes in SV would be related to tennis player's neuromuscular performance. Sixteen competition young tennis players performed 3 testing sessions in a randomized order. In the control session, subjects performed a warm-up protocol followed by the SV and SA tests. The experimental sessions involved 1 (shoulder internal rotation [SHIR]) or 2 (SHIR + shoulder flexion [SHF]) repetitions of a 5 second maximal voluntary isometric contraction (MVIC) executed before the SV and SA tests. Results showed a moderate significant (p = 0.037) difference between SV at control session and following the SHIR + SHF CA protocol at minute 0 (3.4 ± 4.6%; 4.6 km·h-1; ES = 0.711). Serve accuracy did not differ between CA protocols and control session at any time point. No significant relations were found between force-time curve parameters and SV percent changes at different recovery times. Performing 2, short (5 seconds), upper-limb, tennis joint-specific MVIC seems to enhance SV without negatively affecting SA in young competition tennis players. On the contrary, performing one MVIC does not seem to obtain the same effects. Moreover, tennis players with improved neuromuscular performance do not seem to exhibit a better predisposition to postactivation performance enhancement.

Risk Factors for Injury in CrossFit®-A Retrospective Analysis

CrossFit^® is a physical activity program and sport which is based on functional movements performed at high intensity and with high variability of exercises. It develops all motor skills. The study included 424 athletes (266 men and 158 women) from twelve centers in Poland, actively practicing CrossFit^® between 18 and 60 years of age. A questionnaire consisting of 25 questions was used, which was divided into four subsections concerning the characteristics of the sample, training routine, injuries, and information about environment. In total, 48% of respondents participating in the study suffered at least one injury during their entire training history. The injuries suffered most often involved shoulder joint and lumbar spine. Men were found to face a higher risk of injury than women, at 32.78% vs. 15.33% (p = 0.027). The shorter the training period, the smaller the number of injuries observed among the trainees. It was also noted that the shorter the training period, the lower the number of injuries that occurred (p = 0.041). An increase in the number of training sessions per week did not increase the incidence of injuries (p > 0.05). Performing isometric exercises during warm-up reduced the likelihood of injury during CrossFit^® training itself (p = 0.012). Training despite of concomitant acute pain had a significant adverse effect on the incidence of injuries (p = 0.002). The most common risk factors for injury in the CrossFit^® training process include, in particular: gender, training experience, and length of training sessions. Proper warm-up including isometric exercises and training conducted without accompanying pain symptoms reduces the risk of injury.

High-volume intermittent maximal intensity isometric exercise caused great stress, although central motor fatigue did not occur

To establish whether very high-volume, high-intensity isometric exercise causes stress to the body and how it affects peripheral and central fatigue. Nineteen physically active healthy male subjects (21.2 ± 1.7 years; height – 1.82 ± 0.41 m, body weight – 79.9 ± 4.5 kg; body mass index – 24.3 ± 2.1 kg/m2) volunteered to participate in this study. They participated in two experiments 3–5 days apart. Each experiment comprised six series of 60-s maximum voluntary contraction (MVC) force (knee extension) achieved as rapidly as possible. This very high-volume, high-intensity exercise (HVHIE) was performed at different quadriceps muscle lengths: short (SL) and long (LL). The MVC and the electrically stimulated contractile properties of the muscle were measured prior to HVHIE, immediately after and 3 min after each series, and at 3, 10, and 30 min after the end of HVHIE. We found that HVHIE caused high levels of stress (cortisol levels approximately doubled, heart rate and the root mean square successive difference of interval (RMSSD) decreased by about 75%); lactate increased to 8–11 mmol/L, voluntary and 100 Hz stimulation-induced force (recorded immediately after HVHIE) decreased by 55% at LL and 40% at SL. However, the central activation ratio during MVC did not change after either exercise. Isometric HVHIE performed using one leg caused high levels of stress (RMSSD decreased, cortisol increased after HVHIE equally at SL and LL; La increased more while exercising at LL) and the voluntary and electrostimulation-induced muscle force significantly decreased, but muscle central activation during MVC did not decrease.

Sex differences in muscle fatigue following isokinetic muscle contractions

Muscle fatigue is a limiting factor of human performance. It is unclear whether sex-based differences in fatigability exist during dynamic exercise of varying velocities of contraction. We aimed at exploring sex differences in muscle fatigue elicited by maximal isokinetic muscle contractions performed at different angular velocities. Twenty-six healthy participants (13 men: 23.2 ± 1.5; 13 women: 21.9 ± 3.0 years) were tested for concentric knee-extension at slow, moderate and fast angular isokinetic velocity (60, 180 and 300º.s^-1, respectively), on non-consecutive days. The impact of sex on fatigue resistance and consecutive recovery for each isokinetic condition was explored by calculating the percent change in maximal voluntary isometric contraction (MVIC) and in rate of torque development (RTD), from pre- to post-isokinetic exercise (30 repetitions). The isokinetic fatigue index was also determined. No sex differences were obtained in response to isokinetic contractions completed at 60º.s^-1. After performing muscle contractions at 300º.s^-1, women had a significantly greater loss in MVIC than men (- 18.4 ± 5.5 vs. - 12.9 ± 3.8%; p = 0.009) and larger decreases in work output during isokinetic exercise (- 34.2 ± 8.9 vs - 27.5 ± 10.6%; p = 0.017). Recovery of initial MVIC strength was greater for women post-exercise at 180º.s^-1 (15.6 ± 4.1% vs. 6.7 ± 9.5; p = 0.003). No differences were found between sexes in any condition for RTD from pre- to post-fatigue. These results suggest the presence of a sexually dimorphic fatigability in response to dynamic (isokinetic) contractions favouring men at higher absolute velocities of contraction.

INFLUENCE OF MAXIMAL ISOMETRIC STRENGTH ON 20-METER SPRINT TIME

ABSTRACT Introduction The squat is an exercise that is widely used for the development of strength in sports. However, considering that not all sports gestures are vertical, it is important to investigate the effectiveness of propulsive force stimuli applied in different planes. Objective The main purpose of this study was to determine the influence of maximum isometric force (MIF) exerted on starting blocks over performance in 5, 10 and 20-meter sprints. Methods Seven high-level male sprinters (mean age ± SD = 28 ± 5.77 years) participated in this study. The variables were: a) MIF in squats and on starting blocks (measured using a functional electromechanical dynamometer [FEMD]), b) time in 5, 10 and 20-m sprints and c) jump height (measured by the squat jump test). For data analysis, a Pearson correlation was performed between the different variables. The criteria for interpreting the strength of the r coefficients were as follows: trivial (<0.1), small (0.1−0.3), moderate (0.3−0.5), high (0.5−0.7), very high (0.7−0.9), or practically perfect (>0.9). The level of significance was p < 0.05. Results There was very high correlation between MIF exerted on starting blocks and performance in the first meters of the sprint (5-m: r = -0.84, p = 0.01). However, there was small correlation between MIF in squats and performance in the first meters of the sprint (5-m: r = -0.22, p < 0.62). Conclusion The MIF applied on starting blocks correlates very high with time in the first meters of the sprint in high-level athletes. In addition, the use of the FEMD provides a wide range of possibilities for evaluation and development of strength with a controlled natural movement. Level of evidence IV; Prognostic Studies - Case series.

Current Evidence and Practical Applications of Flywheel Eccentric Overload Exercises as Postactivation Potentiation Protocols: A Brief Review

PURPOSE

To summarize the evidence on postactivation potentiation (PAP) protocols using flywheel eccentric overload (EOL) exercises.

METHODS

Studies were searched using the electronic databases PubMed, Scopus, and Institute for Scientific Information Web of Knowledge.

RESULTS

In total, 7 eligible studies were identified based on the following results: First, practitioners can use different inertia intensities (eg, 0.03-0.88 kg·m2), based on the exercise selected, to enhance sport-specific performance. Second, the PAP time window following EOL exercise seems to be consistent with traditional PAP literature, where acute fatigue is dominant in the early part of the recovery period (eg, 30 s), and PAP is dominant in the second part (eg, 3 and 6 min). Third, as EOL exercises require large force and power outputs, a volume of 3 sets with the conditioning activity (eg, half-squat or lunge) seems to be a sensible approach. This could reduce the transitory muscle fatigue and thereby allow for a stronger potentiation effect compared with larger exercise volumes. Fourth, athletes should gain experience by performing EOL exercises before using the tool as part of a PAP protocol (3 or 4 sessions of familiarization). Finally, the dimensions of common flywheel devices offer useful and practical solutions to induce PAP effects outside of normal training environments and prior to competitions.

CONCLUSIONS

EOL exercise can be used to stimulate PAP responses to obtain performance advantages in various sports. However, future research is needed to determine which EOL exercise modalities among intensity, volume, and rest intervals optimally induce the PAP phenomenon and facilitate transfer effects on athletic performances.

Post-activation Potentiation Versus Post-activation Performance Enhancement in Humans: Historical Perspective, Underlying Mechanisms, and Current Issues

Post-activation potentiation (PAP) is a well-described phenomenon with a short half-life (~28 s) that enhances muscle force production at submaximal levels of calcium saturation (i.e., submaximal levels of muscle activation). It has been largely explained by an increased myosin light chain phosphorylation occurring in type II muscle fibers, and its effects have been quantified in humans by measuring muscle twitch force responses to a bout of muscular activity. However, enhancements in (sometimes maximal) voluntary force production detected several minutes after high-intensity muscle contractions are also observed, which are also most prominent in muscles with a high proportion of type II fibers. This effect has been considered to reflect PAP. Nonetheless, the time course of myosin light chain phosphorylation (underpinning “classic” PAP) rarely matches that of voluntary force enhancement and, unlike PAP, changes in muscle temperature, muscle/cellular water content, and muscle activation may at least partly underpin voluntary force enhancement; this enhancement has thus recently been called post-activation performance enhancement (PAPE) to distinguish it from “classical” PAP. In fact, since PAPE is often undetectable at time points where PAP is maximal (or substantial), some researchers have questioned whether PAP contributes to PAPE under most conditions in vivo in humans. Equally, minimal evidence has been presented that PAP is of significant practical importance in cases where multiple physiological processes have already been upregulated by a preceding, comprehensive, active muscle warm-up. Given that confusion exists with respect to the mechanisms leading to acute enhancement of both electrically evoked (twitch force; PAP) and voluntary (PAPE) muscle function in humans after acute muscle activity, the first purpose of the present narrative review is to recount the history of PAP/PAPE research to locate definitions and determine whether they are the same phenomena. To further investigate the possibility of these phenomena being distinct as well as to better understand their potential functional benefits, possible mechanisms underpinning their effects will be examined in detail. Finally, research design issues will be addressed which might contribute to confusion relating to PAP/PAPE effects, before the contexts in which these phenomena may (or may not) benefit voluntary muscle function are considered.