The influence of acute variable resistance loading on subsequent free-weight maximal squat performance

Elastic bands attached to a loaded barbell during a squat exercise create a variable resistance (VR), thus changing the mechanical loading and stress placed through the musculoskeletal system. Preconditioning the neuromuscular system using near-maximal or maximal voluntary contractions (MVC) can induce a phenomenon known as post-activation potentiation (PAP) to enhance performance to ‘supramaximal’ levels. However, the potentiating effects of VR on subsequent free-weight resistance (FWR) squat performance have not been examined. Thus, the aim of the present study was to examine the influence of VR exercise using elastic bands on subsequent FWR squat performance. Sixteen recreationally active men (age = 26.0 ± 7.8 yr, height = 1.7 ± 0.2 m, mass 82.6 ± 12.7 kg) experienced in squatting (>3yr) volunteered for the study after giving written informed consent; ethical approval was granted from the University of Northampton. Subjects’ 1-RM were determined then on two subsequent days either a 3-RM FWR (control) or a 3-RM VR (experimental) squat exercise was performed at 85% 1-RM (35% of the load generated from band tension in the VR condition). Five minutes later, motion analysis recorded knee joint kinematics during a subsequent FWR 1-RM squat, with vastus medialis, vastus lateralis, rectus femoris and semitendinosus electromyograms (EMG) simultaneously recorded. Paired t-tests were used to determine significance, accepted at p0.05) or EMG amplitude (5.9%; p>0.05) occurred. No subjects increased 1-RM in the FWR condition, however 13 of 16 (81%) increased 1-RM by ~10% following VR. Preconditioning the neuromuscular system using VR significantly increased 1-RM without changes in knee extensor muscle activity or knee flexion angle, however eccentric and concentric velocities were reduced. Thus, VR can potentiate the neuromuscular system to enhance subsequent maximal lifting performance. The lack of change in EMG suggests that changes in muscle activity were small or non-existent, which may be explained by force-velocity effects (slower movement = larger forces). Alternatively a greater activation of hip musculature (not measured in the present study) may allow a greater total lower limb force to be developed. Regardless, as 1-RM increased greater lower-limb loading occurred, thus VR potentiated the neuromuscular system and could enhance training stimuli

The influence of 6 weeks of maximal eccentric plantarflexor training on muscle-tendon mechanics

Resistance training can influence muscle-tendon properties including strength, flexibility, stretch tolerance and muscle-tendon stiffness; however the specific influence of eccentric-only training is unknown. Therefore, the aims of the present study were to examine the effects of a 6-week maximal eccentric resistance training programme on isometric plantarflexor moment (MVC), dorsiflexion range of motion (ROM), stretch tolerance (peak passive moment), muscle and tendon stiffness and running economy. Thirteen recreationally active men (age = 20.0 ± 0.9 yr, mass = 75.9 ± 8.5 kg, height = 1.8 ± 0.1 m) volunteered for the study after giving written informed consent; ethical approval was granted from the University of Northampton. Training was performed twice weekly for six weeks and consisted of 5 sets of 12 repetitions of 3-s maximal eccentric contractions at 10°•s-1 from 20° plantarflexion to 10° dorsiflexion. Maximal isometric plantarflexor moment, dorsiflexion ROM, stretch tolerance, and muscle, tendon and muscle-tendon unit (MTU) stiffness were measured using isokinetic dynamometry, real-time ultrasound and 3D motion analyses before and after the training. Running economy (VO2) was determined at a running speed equating to 70%VO2max using online gas analysis. Repeated measures t-tests were used to determine significant differences between pre- and post-training data, significance accepted at p0.05). Analysis of ultrasound data revealed a significant decrease in muscle stiffness (20.6%; p0.05). While the training-induced increase in plantarflexor strength was expected, the substantial increases in ROM, stretch tolerance and tendon stiffness, and the reduction in passive muscle stiffness, were important and novel findings. Interestingly, when measured during passive stretch, MTU stiffness remained unchanged while tendon stiffness increased and muscle stiffness decreased. These disparate findings have clear implications for testing methodologies, and indicate that imaging techniques must be utilised in order to examine the effects of interventions on specific tissues. As the training clearly enhanced the capacity of the muscle to tolerate both tissue loading and deformation, which are commonly associated with muscle strain injury, these data have clear implications for both muscular performance and injury risk

Interactive effects of joint angle, contraction state and method on estimates of Achilles tendon moment arms

The muscle-tendon moment arm is an important input parameter for musculoskeletal models. Moment arms change as a function of joint angle and contraction state and depend on the method being employed. The overall purpose was to gain insights into the interactive effects of joint angle, contraction state and method on the Achilles tendon moment arm using the center of rotation (COR) and the tendon excursion method (TE). Moment arms were obtained at rest (TErest, CORrest) and during a maximum voluntary contraction (CORMVC) at four angles. We found strong correlations between TErest and CORMVC for all angles (0.72 ≤ r ≤ 0.93) with Achilles tendon moment arms using CORMVC being 33 - 36% greater than those obtained from TErest. The relationship between Achilles tendon moment arms and angle was similar across both methods and both levels of muscular contraction. Finally, Achilles tendon moment arms for CORrest were 1 – 8% greater than for CORMVC. [NB rendition of scientific symbols is approximate in this display; please check full text for precise rendition]

Enhancing adaptions to neuromuscular electrical stimulation training interventions

Neuromuscular electrical stimulation (NMES) applied to skeletal muscles is an effective rehabilitation and exercise training modality. However, the relatively low muscle force and rapid muscle fatigue induced by NMES limit the stimulus provided to the neuromuscular system and subsequent adaptations. We hypothesize that adaptations to NMES will be enhanced by the use of specific stimulation protocols and adjuvant interventions

Feasibility, psychosocial effects, influence, and perception of elastic band resistance balance training in older adults

This study utilised feedback from older adults during balance-challenging, elastic band resistance exercises to design a physical activity (PA) intervention. Methods: Twenty-three active participants, aged 51 – 81 years, volunteered to perform a mini balance evaluation test and falls efficacy scale, and completed a daily living questionnaire. Following a 10 min warm-up, participants performed eight pre-selected exercises (1 × set, 8 – 12 repetitions) using elastic bands placed over the hip or chest regions in a randomised, counterbalanced order with 15 min seated rests between interventions. Heart rate (HR) and rate of perceived exertion (RPE) were measured throughout. Participant interview responses were used to qualify the experiences and opinions of the interventions including likes, dislikes, comfort, and exercise difficulty. Results: Similar significant (p \u3c 0.01) increases in HR (pre- = 83 – 85 bpm, mid- = 85 – 88 bpm, post-intervention = 88 – 89 bpm; 5 – 6 %) and RPE (pre- = 8 – 9, mid- = 10, post-intervention = 10 – 11) were detected during the PA interventions (hip and chest regions). Interview data revealed that participants thought the PA interventions challenged balance, that the exercises would be beneficial for balance, and that the exercises were suitable for themselves and others. Participants reported a positive experience when using the PA interventions with an elastic band placed at the hip or chest and would perform the exercises again, preferably in a group, and that individual preference and comfort would determine the placement of the elastic band at either the hip or chest. Conclusion: These positive outcomes confirm the feasibility of a resistance band balance program and will inform intervention design and delivery in future studies

The influence of chain-loaded resistance on subsequent 1-RM free-weight squat performance

Varying the load during a back squat exercise using chains in combination with free-weight resistance (FWR) will manipulate the loading characteristics of the lift. Consequently, this may alter neuromuscular demand and induce post-activation potentiation (PAP). Preconditioning the muscle using near maximal or maximal voluntary contractions can increase force production and improve subsequent strength performance, however the influence of chain-loaded resistance (CLR) on subsequent free-weight squat performance has not been examined. Thus, the aim of the present study was to determine the effects of a chain-loaded resistance warm-up routine on subsequent free-weight squat performance