The acute effects of free-weight and elastic band back squat exercise on subsequent vertical jump performance

Introduction: The back squat exercise is a fundamental exercise for the development of lower limb strength and power. However, in successful attempts of one repetition maximum (1-RM), the upward barbell movement decelerates for a short period referred to as the “sticking point”. The inclusion of elastic bands (EB) minimises the loading during the early concentric phase, while maintaining average loading throughout the lift may limit the impact of the sticking point and enables the athlete to work more closely to maximal throughout a greater range of the lift. Objective: To examine the influence of free-weight resistance (FWR) and EB squat exercise following a comprehensive warm-up on subsequent vertical jump (VJ) performance. Hypothesis: The use of EB during squatting following a comprehensive warm-up would:- (a) enhance subsequent VJ performance; (b) alter VJ mechanics; and (c) increase the neuromuscular activity of the lower limb extensor muscles, when compared to FWR. Methods: Fifteen active men (n=15) visited the laboratory on two occasions under experimental conditions (FWR or EB). After completing a comprehensive warm-up procedure, three maximal VJs were performed and then three consecutive back squat repetitions were completed at 85% of 1-RM using either FWR or EB. Three VJs were then performed 30 s, 4 min, 8 min and 12 min later. During the VJs, knee joint kinematics, ground reaction force data and vastus medialis (VM), vastus (VL) lateralis and gluteus maximus (Glut) electromyograms (EMG) were recorded simultaneously using 3D motion, force platform, and EMG techniques, respectively. Results: No change in any variable was found after the FWR warm-up (p > 0.05). Significant increases (p < 0.05) were detected in CVJ height (5.3-6.5%), net impulse (2.7-3.3%), take-off velocity (2.7-3.8%), peak power (4.4-5.9%), kinetic (7.1-7.2%) and potential (5.4-6.7%) energy, peak (12.9-19.1%) and mean (33.2-35.8%) normalized rate of force development (RFD) following the EB warm-up. Significant increases (p < 0.05) in peak concentric knee angular velocities (3.1-4.1%) and mean concentric VL EMG activity (27.5-33.4%) following the EB warm-up. Discussion: The use of heavy squat lifts with EB increases vertical jump performance following a comprehensive warm-up. The use of EB manipulates the loading characteristics of the squat lift by reducing the effective load near the “sticking point”. This modification in loading allows the athlete to operate at near-maximal levels for a greater proportion of the movement to enhance muscle force output and elicit a greater dynamic muscle performance, which likely provides a greater loading stimulus and may be a more effective training tool even when comprehensive task-specific warm-up is performed

Altered drop jump landing biomechanics following eccentric exercise-induced muscle damage

© 2021 The Authors. Published by MDPI. This is an open access article available under a Creative Commons licence. The published version can be accessed at the following link on the publisher’s website: https://doi.org/10.3390/sports9020024Limited research exists in the literature regarding the biomechanics of the jump-landing sequence in individuals that experience symptoms of muscle damage. The present study investigated the effects of knee localized muscle damage on sagittal plane landing biomechanics during drop vertical jump (DVJ). Thirteen regional level athletes performed five sets of 15 maximal eccentric voluntary contractions of the knee extensors of both legs at 60◦/s. Pelvic and lower body kinematics and kinetics were measured preand 48 h post-eccentric exercise. The examination of muscle damage indicators included isometric torque, muscle soreness, and serum creatine kinase (CK) activity. The results revealed that all indicators changed significantly following eccentric exercise (p< 0.05). Peak knee and hip joint flexion as well as peak anterior pelvic tilt significantly increased, whereas vertical ground reaction force (GRF), internal knee extension moment, and knee joint stiffness significantly decreased during landing (p< 0.05). Therefore, the participants displayed a softer landing pattern following knee-localized eccentric exercise while being in a muscle-damaged state. This observation provides new insights on how the DVJ landing kinematics and kinetics alter to compensate the impaired function of the knee extensors following exercise-induced muscle damage (EIMD) and residual muscle soreness 48 h post-exercise.This research was supported by the postdoctoral scholarship program implemented by University of Thessaly (Greece) and funded by the Stavros Niarchos Foundation, grant number 5394.02.02Published versio

Upper-Body Posture in Adolescent Pianists A Cross-Sectional Study

AIMS: Although the significance of upper-body posture in relation to piano performance has often been highlighted, the role of experience remains unclear. The aim of this study was to examine selected upper body posture parameters in adolescent piano students of different performance level (beginners vs advanced). METHODS: Thirteen (13) adolescent piano students (14.7±0.5 yrs; 7 beginners and 6 advanced) volunteered. They all performed two specific major scales (G-major and E-major) in five octaves in two predetermined different tempi (slow and fast). An upper body biomechanical model consisting of 27 reflective markers was applied on specific bony landmarks. A 10-T camera Vicon system running Nexus 2 was employed to capture upper body motion—a) sway of the trunk in relation to the instrument, b) finger/hand sway over the keyboard, c) overall hand movement, and d) spinal angles—at selected moments of four different performances. RESULTS: Beginners demonstrated more trunk sway than their advanced counterparts (p<0.05), more finger/hand sway (p<0.05), more overall hand movement (p<0.05), and more flexed spinal angles at the start of their performance (p<0.05). Most of these differences appeared in the G-fast performances, whereas the G-slow equivalents revealed no differences. CONCLUSION: Less-experienced piano players are characterized by more movement in their trunk posture and more upper limb activity than their more advanced colleagues. Future research should examine whether interventional programs designed to alter upper-body posture would have beneficial effects in piano performance. © 2020 Science & Medicine

Tibial Rotation Under Combined In Vivo Loading After Single- and Double-Bundle Anterior Cruciate Ligament Reconstruction

Purpose: To evaluate in vivo the differences in tibial rotation between single-and double-bundle anterior cruciate ligament (ACL)-reconstructed knees under combined loading conditions. Methods: An 8-camera optoelectronic system and a force plate were used to collect kinematic and kinetic data from 14 patients with double-bundle ACL reconstruction, 14 patients with single-bundle reconstruction, 12 ACL-deficient subjects, and 12 healthy control individuals while performing 2 tasks. The first included walking, 60 degrees pivoting, and stair ascending, and the second included stair descending, 60 degrees pivoting, and walking. The 2 variables evaluated were the maximum range of internal-external tibial rotation and the maximum knee rotational moment. Results: Tibial rotation angles were not significantly different across the 4 groups (P=.331 and P=.851, respectively) or when side-to-side differences were compared within groups (P=.216 and P=.371, respectively) for the ascending and descending maneuvers, nor were rotational moments among the 4 groups (P=.418 and P=.290, respectively). Similarly, for the descending maneuver, the rotational moments were not significantly different between sides (P=.192). However, for the ascending maneuver, rotational moments of the affected sides were significantly lower by 20.5% and 18.7% compared with their intact counterparts in the single-bundle (P=.015) and double-bundle (P=.05) groups, respectively. Conclusions: High-intensity activities combining stair ascending or descending with pivoting produce similar tibial rotation in single-and double-bundle ACL-reconstructed patients. During such maneuvers, the reconstructed knee may be subjected to significantly lower rotational loads compared with the intact knee. Level of Evidence: Level III, retrospective comparative study

Biomechanics of sit-to-stand transition after muscle damage

The purpose of the study was to examine the effects of exercise-induced muscle damage on the biomechanics of the sit-to-stand transition (STST). Seventeen volunteers participated in an intense, eccentric based, muscle damage protocol of knee flexors and extensors via an isokinetic dynamometer. Kinematic and kinetic data were collected using a 10-camera optoelectronic system and a force plate 24 h before and 48 h after exercise. Statistical analysis showed significant differences in kinematic and kinetic parameters after exercise. Forty-eight hours after exercise, the strategy did change and the knee joint relative effort level increased significantly. Pelvic and hip kinematics, in conjunction with the knee extension joint moment, provided an efficient mechanism to support the participants' locomotor system during the STST. These results may be of great significance in designing supportive devices, as well as composing rehabilitation programs for young or elderly individuals, with various musculoskeletal pathologies. (C) 2012 Elsevier B. V. All rights reserved

Walking kinematics and kinetics following eccentric exercise-induced muscle damage

The goal of this investigation was to investigate how walking patterns are affected following muscle-damaging exercise by quantifying both lower limb kinematics and kinetics. Fifteen young women conducted a maximal isokinetic eccentric exercise (EE) muscle damage protocol (5 x 15) of the knee extensors and flexors of both legs at 60 degrees/s. Three-dimensional motion data and ground reaction forces (GRFs) were collected 24 h pre-EE while the participants walked at their preferred self-selected walking speed (SWS). Participants were asked to perform two gait conditions 48 h post-EE. The first condition (COND1) was to walk at their own speed and the second condition (COND2) to maintain the SWS (+/- 5%) they had 24 h pre-EE. Walking speed during COND1 was significantly lower compared to pre-exercise values. When walking speed was controlled during COND2, significant effects of muscle damage were noticed, among other variables, for stride frequency, loading rate, lateral and vertical GRFs, as well as for specific knee kinematics and kinetics. These findings provide new insights into how walking patterns are adapted to compensate for the impaired function of the knee musculature following muscle damage. The importance to distinguish the findings caused by muscle damage from those exhibited in response to changes in stride frequency is highlighted. (C) 2013 Elsevier Ltd. All rights reserved

Biomechanical effects on lower extremities in human-robot collaborative agricultural tasks

The present study pertains to a key aspect of human-robot collaborative systems which is usually underestimated, namely occupational health prolepsis. The aim of this investigation was to assess the biomechanical effects of manual symmetric load lifting related to a synergistic agricultural task that utilizes an unmanned ground vehicle to undertake the carriage of loads. Towards that goal, kinetic and kinematic data were collected from the lower extremities of thirteen experienced workers, by testing three different deposit heights (70, 80, 90 cm) corresponding to possible adjustments of the available agricultural robot. Moreover, the muscle activation levels of three lower extremity muscles and one trunk muscle were evaluated via a wireless electromyography system. Overall, the experimental findings revealed that the lower examined load height was associated with larger knee flexion moments and hip extension moments. Nevertheless, this height was related to lower activation mainly of the erectus spinae muscles. Finally, insignificant alterations were observed for the ankle joint as well as the activation levels of the other muscles. Consequently, a height equal to 90 cm is suggested, however, by avoiding extreme lumbar postures. The current results can be exploited for possible ergonomic interventions concerning the optimal deposit height of a robotic platform when a similar case is designed. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Three-Dimensional Kinematic and Kinetic Analysis of Knee Rotational Stability After Single- and Double-Bundle Anterior Cruciate Ligament Reconstruction

Purpose: To investigate whether anatomic restoration of the anterior cruciate ligament (ACL) functional bundles results in significant reduction in transverse-plane instability compared with the conventional single-bundle technique during a dynamic 60 pivoting maneuver with the supporting knee in extension. Methods: Using an 8-camera optoelectronic system and a force plate, we examined 10 patients with double-bundle ACL reconstruction, 12 patients with single-bundle reconstruction, 10 ACL-deficient subjects, and 10 healthy control individuals. The 4 groups did not differ in terms of age, body mass index, duration of follow-up, and number of meniscectomies performed. Kinematic and kinetic data were collected from these subjects while performing a pivoting maneuver on each side with the supporting knee in extension. Maximum range of motion for internal-external knee rotation and maximum knee rotational moment were examined. Results: There was no significant difference in tibial rotation either between the 4 groups or between sides. The mean knee rotation for the single-and double-bundle groups was lower than the control group. Rotational moment values were substantially reduced on the affected side of the reconstructed and the ACL-deficient groups. However, rotational moment was not found to affect the degree of angular displacement significantly. Conclusions: Double-bundle ACL reconstruction does not reduce knee rotation further compared with the single-bundle reconstruction technique. The affected side of ACL-deficient or -reconstructed individuals is subjected to reduced knee rotational moments compared with the intact side during stressful functional maneuvers. Level of Evidence: Level III, retrospective comparative study

Variable, but not free-weight, resistance back squat exercise potentiates jump performance following a comprehensive task-specific warm-up

Studies examining acute, high-speed movement performance enhancement following intense muscular contractions (frequently called “post-activation potentiation”; PAP) often impose a limited warm-up, compromizing external validity. In the present study, the effects on countermovement vertical jump (CMJ) performance of back squat exercises performed with or without elastic bands during warm-up were compared. After familiarization, fifteen active men visited the laboratory on two occasions under randomized, counterbalanced experimental squat warm-up conditions: (a) free-weight resistance (FWR) and (b) variable resistance (VR). After completing a comprehensive task-specific warm-up, three maximal CMJs were performed followed by three back squat repetitions completed at 85% of 1-RM using either FWR or VR Three CMJs were then performed 30 seconds, 4 minutes, 8 minutes, and 12 minutes later. During CMJ trials, hip, knee, and ankle joint kinematics, ground reaction force data and vastus medialis, vastus lateralis, and gluteus maximus electromyograms (EMG) were recorded simultaneously using 3D motion analysis, force platform, and EMG techniques, respectively. No change in any variable occurred after FWR (P > 0.05). Significant increases (P < 0.05) were detected at all time points following VR in CMJ height (5.3%-6.5%), peak power (4.4%-5.9%), rate of force development (12.9%-19.1%), peak concentric knee angular velocity (3.1%-4.1%), and mean concentric vastus lateralis EMG activity (27.5%-33.4%). The lack of effect of the free-weight conditioning contractions suggests that the comprehensive task-specific warm-up routine mitigated any further performance augmentation. However, the improved CMJ performance following the use of elastic bands is indicative that specific alterations in force-time properties of warm-up exercises may further improve performance. © 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Lt