Bodyweight squats can induce post-activation performance enhancement on jumping performance:a brief report

Post-activation potentiation enhancement (PAPE) refers to increased force generation following a muscular conditioning pre-activity that acutely enhances subsequent strength and power performance. Athlete apprehension to use heavy weights (i.e. >80%1RM) immediately before a competition or inability to use weights before the performance (e.g. due to regulations) prevent materialising the benefits of PAPE. Therefore, this study examined whether PAPE can be induced with bodyweight squats. Sixteen healthy, team sports players (male: 10, female: 6, mean ± SD: age 22.2 ± 3.0 years, height 1.67 ± 0.08 m, body mass 70.2 ± 8.2 kg) performed three sets of ten repetitions of bodyweight squats with 30 seconds recovery between each set. A countermovement jump was performed 5 minutes before, 2 and 4 minutes after the squat sets and jump height was calculated. The results showed existence of PAPE with the jump height increasing at both 2 (30.8 ± 5.6 cm, p = 0.045, g = 0.21) and 4 (30.8 ± 6.1 cm, p = 0.037, g = 0.20) minutes, compared to baseline (29.5 ± 6.4 cm). This is the first study to use bodyweight squats rather than loaded squats. Our findings indicate that three sets of ten repetitions of squats using bodyweight only can be a sufficient stimulus to induce PAPE

PREVIOUS BALLISTIC AND HEAVY CONDITIONING STIMULI CAN ACUTELY ENHANCE THROWING PERFORMANCE

The purpose of this study was to compare the effects of a ballistic and a heavy load conditioning stimulus on subsequent bench throw performance. Eleven male, competitive rugby players (mean ± SD: body mass 91.5 ± 9.6kg, height 1.79 ± 0.03 m) with at least two years of resistance training exercise performed two ballistic bench throws after warm up. Following a 10-min rest, they performed either a ballistic bench throw (BAL) or a heavy load bench press (HEAVY) conditioning stimulus. Subsequent to a 4-minute rest, they performed another two ballistic bench press throws. No significant differences were revealed for peak power, peak force, rate of force development and force at peak power for either conditioning stimulus. However, significant differences were revealed for bar displacement for the BAL group, and for peak velocity and velocity at peak power for both groups. The results suggest that a ballistic conditioning stimulus can induce post activation performance enhancement and it appears more sport specific in its results than a heavy load conditioning stimulu

Validity and reliability of the Myotest Pro wireless accelerometer in squat jumps

BACKGROUND: Portable and cost-effective accelerometers can yield instantaneous results of force, power, and velocity, with minimum set-up time to assess muscle power. However, such devices must also produce both valid and reliable data. \ud OBJECTIVE: The current study assessed the validity and reliability of the Myotest Pro wireless accelerometer (ACC). \ud METHODS: Thirty physically active males performed two squat jump, on two separate sessions. The jump was recorded simultaneously by a force platform and ACC, which was attached to a barbell resting on the subjects' shoulders. Validity was determined using Pearson correlation coefficient (r) and t-test between the maximum force platform (F_{FP}) and ACC (F_{ACC}) force. Between session reliability of F_{ACC}, power (P_{ACC}) and velocity (V_{ACC}) from the ACC were assessed with t-test, intraclass correlation coefficient (ICC), and coefficient of variation (CV). \ud RESULTS: F_{ACC} correlated highly to F_{FP} (r=0.815, p< 0.05), but there was a proportionate ratio bias of 0.81. There was no difference between sessions (p> 0.05) for any variable. High ICCs were found for all variables (F_{ACC} 0.90; P_{ACC} 0.80; V_{ACC} 0.84). Low CV was found for F_{ACC} (2.1%), P_{ACC} (3.3%) and V_{ACC} (3.2%). \ud CONCLUSIONS: ACC is a valid and reliable tool to use for assessing barbell movement, but caution in power data interpretation is needed

Preferred strength and conditioning coaching leadership behaviours of NCAA Division I and II Collegiate student-athletes based on sex

The present study aimed to examine collegiate student-athletesˈpreferences of leadership behaviours in strength and conditioning (S&amp;C) coaching and evaluate differences between athletesˈpreferred leadership behaviours based on participantsˈsex. 145 (male = 80, female = 65) National Collegiate Athletic Association (NCAA) Division I and II student-athletes aged between 18-25 years, with a mean of 3 (SD = ±1) strength and conditioning sessions per week participated in the study. Participants completed an electronic questionnaire involving the athletesˈ preference version of the Revised Leadership Scale for Strength and Conditioning (RLSSC). Summary statistics revealed that the most preferred behaviour was ˈtraining and instructionˈ, median of 4.5 (IQR = 1.0), and the least preferred was ˈautocraticˈ, median of 2.0 (IQR = 0.5). Similar results were observed for both groups. Males preferred autocratic behaviour more than females (male = 2.5, female = 2.0). Statistically significant difference was identified between groups for autocratic behaviour (p = .001). Effect sizes indicated that the magnitude of differences between groups was small or moderate, with the highest value for autocratic behaviour (d = 0.5). The observation of marginal statistically significant difference aligns with previous research, suggesting sex-related differences. However, small and moderate effect sizes indicate that differences are not practically significant enough to encourage distinct coaching approaches. This study sheds light on the preferences of coaching behaviours among student-athletes in strength and conditioning coaching. The findings emphasise the importance of positive psychosocial behaviours such as training and instruction, positive feedback, situational considerations and social support. While there were slight differences between the sexes, results suggested that both groups valued positive coaching behaviours. These findings provide implications for coaching practice and offer a basis for further research to explore leadership coaching behaviours in strength and conditioning

The acute effects of intracomplex rest intervals on rate of force development and ballistic performance responses following strength-power complex training in talent-identified adolescent rugby players

This study investigated the effects of a strength-power complex on subsequent ballistic activity (BA) performance responses across a profile of jumps in adolescent talent-identified rugby players. Rate of force development (RFD) and BA performance responses was recorded in 22 participants over four intracomplex rest intervals (ICRI) (15s, 30s, 45s, 60s) following a complex of 3 repetitions of back squat @80% 1RM and 7 countermovement jumps (CMJs) in a randomised, counterbalanced design. Within subjects, repeated measures ANOVAs were conducted on peak rate of force development (PRFD), time to peak rate of force development (TPRFD), peak force (PF), and time to a peak force (TPF). Confidence limits were set at ±90% and effect size across the sample (partial ɳ²) was calculated across P1-P4 for all jump profiles. No significant effects were observed across jump profiles or ICRI. The research confirms RFD and BA performance responses were maintained across all jump profiles and each ICRI. In contrast to previous research, the use of minimal ICRI of 15s, 30s, 45s and 60s following strength-power complex training is a practical time-efficient means of maintaining RFD and BA performance responses across jump profiles of seven jumps, which has important implications in practical coaching environments

Systolic and Diastolic Left Ventricular Mechanics during and after Resistance Exercise

PURPOSE: To improve the current understanding of the impact of resistance exercise on the heart, by examining the acute responses of left ventricular (LV) strain, twist and untwisting rate ('LV mechanics'). METHODS: LV echocardiographic images were recorded in systole and diastole before, during and immediately after (7-12 s) double leg press exercise at two intensities (30% and 60% of maximum strength, 1-repetition-maximum, 1RM). Speckle tracking analysis generated LV strain, twist and untwisting rate data. Additionally, beat-by-beat blood pressure was recorded and systemic vascular resistance (SVR) and LV wall stress were calculated. RESULTS: Responses in both exercise trials were statistically similar (P > 0.05). During effort, stroke volume decreased while SVR and LV wall stress increased (P 0.05). Immediately following exercise, systolic LV mechanics returned to baseline levels (P < 0.05) but LV untwisting rate increased significantly (P < 0.05). CONCLUSIONS: A single, acute bout of double leg-press resistance exercise transiently reduces systolic LV mechanics, but increases diastolic mechanics following exercise, suggesting that resistance exercise has a differential impact on systolic and diastolic heart muscle function. The findings may explain why acute resistance exercise has been associated with reduced stroke volume but chronic exercise training may result in increased LV volumes

The effect of an acute bout of resistance exercise on carotid artery strain and strain rate

Arterial wall mechanics likely play an integral role in arterial responses to acute physiological stress. Therefore, this study aimed to determine the impact of low and moderate intensity double-leg press exercise on common carotid artery (CCA) wall mechanics using 2D vascular strain imaging. Short-axis CCA ultrasound images were collected in 15 healthy men (age: 21 ± 3 years; stature: 176.5 ± 6.2 cm; body mass; 80.6 ± 15.3 kg) before, during, and immediately after short-duration isometric double-leg press exercise at 30% and 60% of participants’ one-repetition maximum (1RM: 317 ± 72 kg). Images were analyzed for peak circumferential strain (PCS), peak systolic and diastolic strain rate (S-SR and D-SR) and arterial diameter. Heart rate (HR), systolic and diastolic blood pressure (SBP and DBP) were simultaneously assessed and arterial stiffness indices were calculated post hoc. A two-way repeated measures ANOVA revealed that during isometric contraction, PCS and S-SR decreased significantly (P < 0.01) before increasing significantly above resting levels post-exercise (P < 0.05 and P < 0.01 respectively). Conversely, D-SR was unaltered throughout the protocol (P = 0.25). No significant differences were observed between the 30% and 60% 1RM trials. Multiple regression analysis highlighted that HR, BP and arterial diameter did not fully explain the total variance in PCS, S-SR and D-SR. Acute double-leg press exercise is therefore associated with similar transient changes in CCA wall mechanics at low and moderate intensities. CCA wall mechanics likely provide additional insight into localized intrinsic vascular wall properties beyond current measures of arterial stiffness

In vivo human cardiac shortening and lengthening velocity is region-dependent and not coupled with heart rate

New Findings •What is the central question of this study? Regulation of cardiac function is typically achieved by changes in heart rate (HR) and cardiac shortening velocity (strain rate; SR), but their interdependence in vivo remains poorly understood. •What is the main finding and its importance? Using resistance exercise to increase heart rate and arterial resistance physiologically in humans and measuring regional cardiac SR (at the base and apex), we found that HR and SR were not strictly coupled because SR at the base and apex responded differently, despite the same HR. Importantly, our data show that the region-averaged ‘longitudinal’ SR, which is currently popular in the clinical setting, markedly underestimates the contribution of the apex. The fundamental importance of cardiac shortening and lengthening velocity (i.e. strain rate; SR) has been demonstrated in vitro. Currently, the interdependence between in vivo SR and HR is poorly understood because studies have typically assessed region-averaged ‘longitudinal’ strain rate, which is likely to underestimate the apical contribution, and have used non-physiological interventions that may also have been influenced by multicollinearity caused by concomitant reductions in arterial resistance. Resistance exercise acutely raises HR, blood pressure and arterial resistance and transiently disassociates these cardiovascular factors following exercise. Therefore, we measured SR, HR, blood pressure and arterial resistance in nine healthy men (aged 20 ± 1 years) immediately before, during and after double-leg-press exercise at 30 and 60% of maximal strength. Resistance exercise caused a disproportionate SR response at the left ventricular base and apex (interaction effect, P < 0.05). Consequently, associations between HR and regional peak SR were inconsistent and mostly very weak (r2 = 0.0004–0.24). Likewise, the areas under the curve for systolic and diastolic SR and their relationship with systolic and diastolic duration were variable and weak. Importantly, region-averaged ‘longitudinal’ SR was identical to basal SR, thus, markedly underestimating the apical contribution. In conclusion, in vivo HR and SR are not strictly coupled in healthy humans, which is explained by the region-specific responses of SR that are not captured by ‘longitudinal SR’. This novel observation emphasizes the independent role of in vivo SR in overall cardiac function during stress and may cause a ‘revival’ of SR as a marker of regional left ventricular (dys)function

Effect of back squat depth on lower-body postactivation potentiation

Postactivation potentiation (PAP) refers to increased muscular force generation after previous muscular activity. Various studies have used different squat variations as a PAP stimulus; however, different squat depths can have different mechanical and physiological demands that could yield different PAP levels and subsequent performance. The study aimed to compare the effects of the parallel (PS) and quarter (QS) squat on PAP. Twenty-seven, semiprofessional, male rugby union players (mean 6 SD, 18 6 2 years, 87.2 6 5.4 kg, 180.7 6 5.1 cm) performed a countermovement jump (BL-CMJ) followed by a 10-minute rest. Subsequently, they performed 3 PS or QS, at each squat's respective 3-repetition maximum load, in a randomized counterbalanced order. After a 5-minute rest, another countermovement jump (CMJ) was performed (POSTCMJ). Countermovement jump height (JH), peak power (PP), impulse (I), and flight time (FT) were recorded using a contact mat. BL-CMJ and POST-CMJ pairwise comparisons for all variables were conducted for each squat type to examine performance changes. Delta values were compared to examine whether one squat produced better CMJ results. Both squats induced PAP for all the variables (p , 0.05), although PS produced better results than QS (p , 0.05; JH, 4.6 6 2 vs. 3.5 6 2 cm; I, 15 6 6 vs. 12 6 5 N·s; PP, 285 6 109 vs. 215 6 96 W; FT, 34 6 23 vs. 26 6 11 milliseconds for PS vs. QS). This is the first study to demonstrate that different squat types can induce PAP and that PS is more beneficial for subsequent CMJ performance compared with QS. It is suggested that the deeper depth of PS, which increases gluteus maximum activation and work produced, is responsible for the increased CMJ performance