Acute Effects of Intracontrast Rest After Back Squats on Vertical Jump Performance During Complex Training.

ABSTRACT: Houlton, LJ, Moody, JA, Bampouras, TM, and Esformes, JI. Acute effects of intracomplex rest after back squats on vertical jump performance during complex training. J Strength Cond Res XX(X): 000-000, 2024-Postactivation performance enhancement and complex-contrast sets are prevalent in sports science research. Typical complex-contrast sets consist of heavy back squats, an intracontrast rest period (ICRP) and vertical jumps (countermovement jumps [CMJs], or squat jumps [SJs]). Propulsive impulse (Jprop) is considered the leading indicator of jump performance. However, studies evaluating jump performance during complex-contrast sets use jump height as the primary performance measure, limiting insight into ICRP's effect on jump performance. We assessed the effect of a 3 repetition maximum (3RM) back squat and 6 ICRPs on vertical jump Jprop and associated force-time components. Fourteen subjects completed 12 experimental conditions, assigned equally to 4 testing sessions. Independent variables, in a 6 × 2 randomized, counterbalanced design, were ICRP (0, 60, 120, 180, 240, 300 seconds; ICRP0, ICRP60, ICRP120, ICRP180, ICRP240, ICRP300, respectively) and vertical jump (CMJ and SJ). Conditions consisted of baseline vertical jumps, followed by 3 back squat repetitions at 100% 3RM, an ICRP and experimental jumps. Symmetrized percentage changes between experimental and baseline jumps were assessed using repeated measures analysis of variance (ANOVA) and pairwise effect sizes. Results showed significant effects (p ≤ 0.05) on CMJ average rate of force development (RFD) between ICRP0 and ICRP120 and ICRP0 and ICRP300. Pairwise comparisons showed medium and large effect sizes for and increases in CMJ RFD (g = 0.83-2.69) whereas SJ RFD decreased (g = 0.81-2.57). Small effect sizes were found for Jprop, peak force, and mean force. Results suggest limited change in Jprop (g = 0.01-0.58), but back squats may potentiate RFD via the stretch-shortening cycle.

Integrating Resistance Training Into Secondary School Physical Education Lessons: Effects of a 6-Week Intervention on Athletic Motor Skill Competencies.

PURPOSE: The purpose of this study was to examine the effects of resistance training (RT) in physical education lessons on athletic motor skill competencies in secondary school children. METHOD: Seventy-eight males were randomized into experimental year groups or a control group. Experimental groups participated in RT during physical education lessons for a 6-week half-term. The control group continued with their games-based curriculum. Countermovement jump (CMJ) height, seated medicine ball throw (SMBT) distance, and RT skills battery scores were measured preintervention and postintervention. RESULTS: All experimental groups significantly improved SMBT distance and RT skills quotient (P < .05). All intervention year groups also significantly improved CMJ height (P < .05), except for year 9. Although the control group did not show improvements in CMJ height and RT skills quotient, there was a significant improvement in SMBT distance (P < .05). The year 7 and 8 males exhibited greater improvements in CMJ height and SMBT distance (d = 0.21-0.79) than in year 9 (d = 0.00-0.40). CONCLUSION: Results of the study indicated that a 6-week half-term RT intervention in physical education lessons can improve athletic motor skill competencies (P < .05, d = 0.21-2.51) in male youths.

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, 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. RESULTS: Responses in both exercise trials were statistically similar (P > 0.05). During effort, stroke volume decreased, whereas SVR and LV wall stress increased (P < 0.05). Immediately after effort, stroke volume returned to baseline, whereas SVR and wall stress decreased (P < 0.05). Similarly, acute exercise was accompanied by a significant decrease in systolic parameters of LV muscle mechanics (P < 0.05). However, diastolic parameters, including LV untwisting rate, were statistically unaltered (P > 0.05). Immediately after 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 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.

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.

Influence of exercise training mode on arterial diameter: A systematic review and meta-analysis.

OBJECTIVES: To examine whether differences in arterial diameter exist between athletes participating in endurance, resistance or mixed exercise training. DESIGN: A systematic review with meta-analysis. METHODS: 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). RESULTS: Compared to controls, endurance athletes displayed the greatest difference in diameter in the brachial artery (δ=1.84, 95% CI: 0.59, 3.09, p<0.01), whereas for mixed athletes, the greatest difference in diameter occurred in the femoral artery (δ=3.65, 95% CI: 2.21, 5.10, p<0.01), 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, p<0.01) than controls, however differences in other vessels could not be determined through meta-analysis due to insufficient data. CONCLUSIONS: 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.

In vivo human cardiac shortening and lengthening velocity is region dependent and not coupled with heart rate: 'longitudinal' strain rate markedly underestimates apical contribution.

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 (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.

Breathing pattern disorders and functional movement.

STUDY DESIGN: Experimental design. BACKGROUND: Normal breathing mechanics play a key role in posture and spinal stabilization. Breathing Pattern Disorders (BPD) have been shown to contribute to pain and motor control deficits, which can result in dysfunctional movement patterns. The Functional Movement Screen™ (FMS™) has been shown to accurately predict injury in individuals who demonstrate poor movement patterns. The role BPD play on functional movement is not well established. Furthermore, there is currently no single test to clinically diagnose BPD. A variety of methods are used, but correlations between them are poor. PURPOSE: To examine the relationship between BPD and functional movement and identify correlations between different measures of BPD. METHODS: Breathing was assessed in 34 healthy individuals using a multi-dimensional approach that included biomechanical, biochemical, breathing related symptoms, and breathing functionality measures. Movement was assessed using the FMS™. Analysis, involving independent t-tests and Pearson correlation were performed to identify associations between measures. RESULTS: Individuals who exhibited biochemical and biomechanical signs of BPD were significantly more likely to score poorly on the FMS™. These studied measures of BPD correlated highly with each other. CONCLUSION: These results demonstrate the importance of diaphragmatic breathing on functional movement. Inefficient breathing could result in muscular imbalance, motor control alterations, and physiological adaptations that are capable of modifying movement. These findings provide evidence for improved breathing evaluations by clinicians. LEVEL OF EVIDENCE: 2B.

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 ± 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.

Effect of different types of conditioning contraction on upper body postactivation potentiation.

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 (post-BBPT). 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 <7 seconds for DYN). Peak power (Ppeak), peak force (Fpeak), maximum distance (Dmax) and rate of force development (RFD) were measured using a linear position transducer. Electromyography (EMG) of the pectoralis major and triceps brachii was also recorded. The ISO produced significantly higher Ppeak (587 ± 116 and 605 ± 126 W for pre- and post-BBPT, respectively; p < 0.05). No significant differences in Ppeak were revealed for CON, ECC, and DYN (p > 0.05), and no significant differences existed in Fpeak, Dmax, and RFD for ISO, CON, ECC, and DYN (p > 0.05). Finally, EMG was not significantly different between pre- and post-BBPT 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.

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.

The influence of menstrual cycle phase upon postexercise hypotension.

PURPOSE: 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. METHODS: 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. RESULTS: Cardiovascular parameters did not differ between menstrual phases at rest (P > 0.05). 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; P < 0.05). Postexercise cardiac output, stroke volume, ejection fraction, left ventricular dimensions, and heart rate did not differ across menstrual phases (P > 0.05). 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 (P < 0.05). 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 (P < 0.05). CONCLUSION: Buffering of PEH appears to be enhanced in the LF and ML phases of the cycle where estrogen concentrations are known to be elevated.

Measurement of human muscle volume using ultrasonography.

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<0.05). The ULT and MRI methods gave similar results [mean (SD) ULT: 133.2 (20) cm(3); MRI: 131.8 (18) cm(3)]. Nevertheless, a systematic bias of 3.33 cm(3) and a random error of 3.53 cm(3) were found when using the ULT method compared with the MRI method, which results in an error of -0.15% to 5.17%. We conclude that the ULT method is a reproducible and valid method for the estimation of human muscle volume.