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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.

The effect of head positioning is often not accounted for when optimising performance in the back squat exercise. The primary aim of the study was to identify the most advantageous head position for peak power (PP), peak velocity (PV) and peak force (PF) performance in the back squat exercise. A secondary aim was to identify the most favourable head position. Twenty male rugby union players performed 1x3 repetitions at 75% one repetition maximum (1RM) to determine their preferred pre-intervention head position, followed by 1x3 at 75% 1RM in a flexed (FP), extended (EP) and neutral (NP) neck position, performed in a counterbalanced and randomised order. PP, PV, PF and comfort level (CL) were measured during each repetition. FP resulted in significantly higher PP (3147.50 ± 464.70 W; p

Muscular performance is influenced by its contractile history, with fatigue being the most noticeable effect, reflected in the inability of the neuromuscular system to maintain or generate the expected force requirements of an activity. Postactivation potentiation (PAP) was initially examined by assessing muscle twitch force, with twitch potentiation being well established. Post-tetanic and PAP have been studied for more than a century, ranging from studies examining animal muscle preparations to human skeletal muscle in vitro and in vivo. Acute training methods and techniques aim to achieve positive short-term responses that over time accumulate and lead to long-term improvements in performance. PAP is a well-established phenomenon with a long research history. To capitalise on this phenomenon, research studies and practitioners have tried to improve performance both acutely and long-term by coupling strength with power-based exercises to enhance the latter.

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.

This article was published in Experimental Physiology on 6 May 2015 (online), freely available at http://dx.doi.org/10.1113/EP085081

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").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, one-repetition maximum). 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.Responses in both exercise trials were statistically similar (P0.05). During effort, stroke volume decreased, whereas SVR and LV wall stress increased (P0.05). Immediately after effort, stroke volume returned to baseline, whereas SVR and wall stress decreased (P0.05). Similarly, acute exercise was accompanied by a significant decrease in systolic parameters of LV muscle mechanics (P0.05). However, diastolic parameters, including LV untwisting rate, were statistically unaltered (P0.05). Immediately after exercise, systolic LV mechanics returned to baseline levels (P0.05) but LV untwisting rate increased significantly (P0.05).A single, acute bout of double-leg press resistance exercise transiently reduces systolic LV mechanics, but increases diastolic mechanics after 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.

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 \ud Objective: The current study assessed the validity and reliability of the Myotest Pro wireless accelerometer (ACC). \ud \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 \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 \ud Conclusions: ACC is a valid and reliable tool to use for assessing barbell movement, but caution in power data interpretation is needed.

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 (r(2) = 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.

To examine whether differences in arterial diameter exist between athletes participating in endurance, resistance or mixed exercise training.A systematic review with meta-analysis.Random effects meta-analyses of the weighted mean difference in aortic, carotid, brachial and femoral arterial diameters, height and body mass were conducted on data from 16 peer-reviewed studies indexed on PubMed, MEDLINE, SCOPUS and Sport Discus. Effect sizes were calculated as the standardised difference in means (δ), and used to compare endurance (n=163), resistance (n=192), and mixed trained athletes (n=360), with controls (n=440).Compared to controls, endurance athletes displayed the greatest difference in diameter in the brachial artery (δ=1.84, 95% CI: 0.59, 3.09, p0.01), whereas for mixed athletes, the greatest difference in diameter occurred in the femoral artery (δ=3.65, 95% CI: 2.21, 5.10, p0.01), despite there being no differences in height or body mass between these groups. Resistance athletes had a significantly greater body mass (p=0.047) and aortic diameter (δ=1.81, 95% CI: 1.58, 2.05, p0.01) than controls, however differences in other vessels could not be determined through meta-analysis due to insufficient data.Our results provide evidence for localised arterial differences, which occur more extensively in peripheral vessels (brachial and femoral). Chronically, vascular remodelling may occur as a result of the specific haemodynamic conditions within each vessel, which likely differs depending on the mode of exercise. In the future, empirical research is needed to understand the effect of resistance training on chronic vascular remodelling, as this is not well documented.

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 ± SD, 18 ± 2 years, 87.2 ± 5.4 kg, 180.7 ± 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 (POST-CMJ). 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 ± 2 vs. 3.5 ± 2 cm; I, 15 ± 6 vs. 12 ± 5 N·s; PP, 285 ± 109 vs. 215 ± 96 W; FT, 34 ± 23 vs. 26 ± 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.

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

Muscle contractions preceding an activity can result in increased force generation (postactivation potentiation [PAP]). Although the type of muscular contractions could affect subsequent strength and power performance, little information exists on their effects. The purpose of this study was to examine PAP effects produced by isometric (ISO), concentric (CON), eccentric (ECC), or concentric-eccentric (DYN) conditioning contractions on upper body force and power performance. Ten male, competitive rugby players (mean ± SD: age 20.4 ± 0.8 years, height 177.0 ± 8.1 cm, body mass 90.2 ± 13.8 kg) performed a ballistic bench press throw (BBPT) followed by a 10-minute rest and one of the conditioning contractions. After a 12-minute rest, the subjects performed another BBPT (postBBPT). The conditioning contractions, applied on separate days and in counterbalanced randomized order, were a 7-second isometric barbell bench press for ISO and 1 set of 3 bench press repetitions at 3 repetition maximum for CON, ECC, and DYN (each repetition lasting 2 seconds for CON and ECC, overall execution time 0.05), and no significant differences existed in F^sub peak^, D^sub max^, and RFD for ISO, CON, ECC, and DYN (p > 0.05). Finally, EMG was not significantly different between pre- and postBBPT for any of the conditioning contractions (p > 0.05). Isometric contractions appear to be the only conditioning contractions increasing upper body power output after long resting periods.

Postactivation potentiation following different modes of exercise. J Strength Cond Res 24(7): 1911-1916, 2010-The performance characteristics of skeletal muscle are transient in nature and have been shown to be significantly affected by its contractile history, where the phenomenon of acute enhancement is termed postactivation potentiation (PAP). Acute enhancement of dynamic activity has been observed when preceded by resistance exercises; however little information exists for plyometric activity as a conditioning stimulus. In addition, no study has examined PAP effects on more than one subsequent performance trial. The purpose of the present study was to determine whether countermovement jump (CMJ) performance could be enhanced if preceded by heavy-resistance exercise or by dynamic plyometric activity over 3 trials. Thirteen anaerobically trained male subjects (mean ± SD: age, 22 ± 3 years; height, 182.4 ± 4.3 cm; body mass, 82.7 ± 9.2 kg) performed in a counterbalanced order 3 half squats using a 3 repetition maximum loading (SQUAT), a set of 24 contacts of lower body plyometric exercises (PLYO), or a control of no activity (REST) 5 minutes before each CMJ. Three sets of each treatment and CMJ were performed in total and maximal displacement (dmax), peak power (Ppeak), and peak vertical force (Fpeak) were recorded, whereas rate of force development and relative force (F/body mass) were calculated for every trial. No significant differences were revealed for any of the other variables, but greater displacement was found for SQUAT compared to REST or PLYO, whereas no differences were revealed for any of the conditions for the repeated trials. Although heavy resistance-induced PAP seems to enhance jump height compared to REST or PLYO in repeated CMJ performance, it has no additional benefit on repeated trials.

Postexercise hypotension (PEH) has been observed in males and females; however, the impact of menstrual cycle phase upon PEH has not been evaluated. We examined the pattern of PEH in the early follicular (EF), late follicular (LF), and midluteal (ML) phases of the menstrual cycle in eight eumenorrheic women following 30 min of exercise at 80% lactate threshold.Supine hemodynamic measurements were assessed at rest and then for 45 min following exercise. Blood pressure was measured with manual sphygmomanometry, calf vascular resistance (CVR) via venous occlusion plethysmography, and central hemodynamics with echocardiography.Cardiovascular parameters did not differ between menstrual phases at rest (P0.05). The pattern of PEH was unaffected by menstrual phase, but mean arterial and diastolic (DBP) pressures dropped to significantly lower levels across the recovery period in the EF phase than in the LF and ML phases (mean DBP EF: 69 +/- 4; LF 74 +/- 3; ML 72 +/- 5; P0.05). Postexercise cardiac output, stroke volume, ejection fraction, left ventricular dimensions, and heart rate did not differ across menstrual phases (P0.05). These parameters, except for left ventricular dimensions in systole and heart rate, varied with recovery time, increasing to a peak between 5 and 10 min postexercise (P0.05). CVR displayed a significant interaction between cycle phase and recovery time as resistance increased to greater values in the ML phase compared with the EF and LF phases following 30 min of postexercise recovery (P0.05).Buffering of PEH appears to be enhanced in the LF and ML phases of the cycle where estrogen concentrations are known to be elevated.

The volume of the human tibialis anterior (TA) muscle was estimated in vivo by ultrasonography (ULT) and by magnetic resonance imaging (MRI) in six subjects. In both methods, 11 axial scans were taken along the muscle belly, and the cross-sectional area of the muscle in each scan was digitised. Muscle volume was calculated by treating the muscle as a series of truncated cones. To assess the reproducibility of the ULT method, all subjects were scanned twice. A high test-retest reliability was found ( R(2)=0.99), with the two ULT measurements being significantly correlated with each other ( P

Assessing strength and power is crucial for evaluating muscular performance and function. As laboratory testing can be time-consuming or inaccessible to many athletes, portable accelerometers have been developed to assess strength and power on the field. Recently, a wireless accelerometer was introduced to allow for even greater flexibility in assessment. Nevertheless, any assessment tool must be valid and reliable. The aim of the current study was to assess the validity and reliability of a commercially available accelerometer. Forty-eight physically active subjects (males, n=32: age 29.2±8.8 yrs, height 1.79±0.12 m, body mass 82.0±14.3 kg; females, n=16: age 27.4±6.3 yrs, height 1.71±0.06 m, body mass 63.8±7.4 kg) completed two countermovement jump squats on a force plate (FP) with at least one minute rest, on two separate occasions. The accelerometer was secured on a lightweight bar, which rested on the subjects’ shoulders whilst jumping. The jump with the highest force generation was selected from each occasion for further analysis. Validity was determined from the Pearson correlation coefficient (r) between the accelerometer and the FP. Bias was also calculated, using a t-test. Reliability was assessed by the intraclass correlation coefficient (ICC) and coefficient of variation (CV), whilst test-retest differences were examined with a t-test. The accelerometer demonstrated significant and high correlation to the force plate (p=0.001, r=0.85), whilst it overestimated force production by 7.8% (p=0.001). Repeatability for both devices was the same (ICC=0.87), with small CV (accelerometer=7.5%, FP=6.1%) and test-retest differences (accelerometer=0.1%, FP=1.1%). The results indicate that the Myotest Pro® accelerometer is a valid and reliable tool for assessing force in the field. However, caution needs to be exercised when the results are compared to data obtained from a force plate, as the Myotest Pro® calculation method overestimates the maximum force produced.