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

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

Impact of static stretch and muscular contractions on force production within the human triceps surae muscle-tendon complex

Pre-performance routines commonly include stretching and intense muscular contractions in an attempt to optimise muscular performance and reduce injury risk. However, the isolated and combined effects of stretching and muscle contractions on neuromuscular performance are not well described. The aims of this research were to examine the effects of acute static stretch and intense muscular contractions on force production of the human plantarflexors and to examine possible mechanical and neuromuscular mechanisms underpinning any changes. Techniques including isokinetic dynamometry, electromyography (EMG), sonography and motion analysis were used in three studies on recreationally active human volunteers (n=20). In the first study, three 60-s passive stretches was found to significantly reduce concentric plantarflexor joint moment (5.0%; P\u3c0.05), which was correlated (r = 0.81; P\u3c0.01) with a reduction in EMG amplitude (9.2%; P\u3c0.05). No reduction in Achilles tendon stiffness or gastrocnemius medialis (GM) muscle operating length was found, and all measures recovered by 30 min. This indicates that post-stretch force losses are transient and are largely associated with reduced neuromuscular activity (EMG amplitude) rather than changes in the muscles’ operating lengths. Nonetheless, strong muscular contractions, commonly performed during preperformance routines and incorporated into research designs, may influence the effects of stretch. In the second study it was found that six 8-s maximal isometric contractions reduced Achilles tendon stiffness (10.9%; P\u3c0.01) and passive joint moment (4.9%; P\u3c0.01) and also significantly reduced concentric moment (11.5%; P\u3c0.01), which was again correlated (r = 0.90; P\u3c0.01) with a reduction in EMG amplitude (21.0%; P\u3c0.01). Importantly, a subsequent bout of static stretch, which was identical to that used in study 1, did not result in a further change in any measure (P \u3e 0.05). Whilst concentric moment and EMG recovered 30 min later, the decreases in Achilles tendon stiffness and passive moment remained. Thus, the normal stretch-induced reductions in force production were removed when isometric contractions were performed prior to stretch, but this was because concentric strength and neuromuscular activity were already affected; the reduction in concentric moment without a decrease in isometric moment indicates a contraction mode-specific response. The final study revealed that the use of concentric contractions (6×8-s) also resulted in similar reductions in Achilles tendon stiffness (11.7%; P\u3c0.01) and concentric joint moment (6.6%; P\u3c0.01) as the isometric contractions, and these were correlated (r = 0.94; P\u3c0.01) with a reduction in EMG amplitude (10.2%; P\u3c0.01). However, a further reduction in concentric moment was detected following an identical bout of static stretch (5.8%; P\u3c0.01) with no further change in EMG. Importantly, EMG recovered 30 min later while concentric moment remained depressed (9.2%; P\u3c0.01), indicating a musclebased mechanism for these force losses. No reduction in GM muscle operating length was found, removing this as a mechanism underpinning the losses in force. The findings from the present series of studies have important implications for research study design as the warm-up imposed on subjects prior to stretch seems to strongly influence the impact of stretch. Furthermore, the results also have important practical implications in the formulation of preperformance routines where maximal force production in the plantarflexors is an important goal

Recommendations for high intensity upper body exercise testing

Introduction: For given submaximal and maximal peak power outputs aerobic responses to upper body exercise are different to those for lower body exercise (Sawka, 1986: Exercise & Sport Sciences Reviews, 14, 175-211). However, much less is known regarding responses to exercise intensities at and around peak oxygen up take (VO2peak). Purpose: The purpose of this study was to determine the metabolic responses during arm crank ergometry (ACE) below, at and above peak oxygen uptake and to help establish exercise testing guidelines for high intensity upper body exercise. Methods: Following institutional ethical approval fourteen male students (Age 21.1, s = 6.1 years and 2.44 s=0.44 VO2peak) volunteered to take part in this study. Each participant exercised on a table mounted cycle ergometer (Monark 894E, Monark Exercise AB, Sweden). After habituation peak minute power (PMP) was calculated from an incremental test. Subsequently each participant completed four continuous work tests (CWT) to volitional exhaustion at 80%, 90%, 100% and 110% of PMP. All tests were completed at 70 rev∙min-1 with a minimum of 48-h between tests and the order was counterbalanced. Each CWT was preceded by a 5 min warm-up, loaded with a mass corresponding to the participants 80% PMP for 20 s at minutes 2, 3 and 4. Oxygen uptake (VO2), respiratory exchange ratio (RER), heart rate (HR) and ratings of perceived exertion for the arms (local (RPEL) and cardiorespiratory strain (RPECR) were recorded at 1 min, 2 min and at volitional exhaustion. The EMG responses at three sites (flexor carpi ulnaris, biceps brachii and triceps brachii lateral) were recorded using double-differential (16-3000 Hz bandwidth, x300 gain), bipolar, active electrodes (MP-2A, Linton, Norfolk, UK). Electromyographic data were sampled at 1000 Hz and filtered using a 20 to 500 Hz band-pass filter (MP150 Data Acquisition and AcqKnowledge 4.0, Biopac, Goleta, CA). The EMG signals for each muscle were root mean squared (RMS) with a 500-ms sample window. The signal was then normalised, prior to each CWT, as a percentage of the mean of 3 sets of 10 duty cycles completed during the warm-up (see above) when the participants 80% PMP for 20 s was applied. Time to exhaustion (Tlim) was recorded as the performance outcome measure. Data for Tlim were analysed using one-way analysis of variance. Differences in EMG, VO2, RER, HR, RPEL and RPECR were analysed using separate two-way analysis of variance with repeated measures (trial x time). All analyses were performed using the Statistical Package for Social Sciences ( 17.0; SPSS Inc., Chicago, IL). Individual differences in means were located using Bonferroni post-hoc correction. Significance was accepted at P < 0.05. Results: As resistive load increased Tlim decreased (611 s=194, 397 s=99, 268 s=90, 206 s=67s, respectively; P < 0.001, ES = 0.625). Post-hoc analysis revealed that Tlim using 80%PMP was longer than for 90%, 100% and 110% PMP trials (P < 0.001) and 90% was longer than both 100% and 110% PMP trials (P = 0.079, P = 0.001). At exhaustion VO2 was similar across trials (P = 0.413, ES = 0.053), although 80% PMP VO2 tended to be less (2.10 s=0.32 l·min-1) than for 90% (2.29 s=0.37), 100% (2.33 s=0.49) and 110% (2.26 s=0.34). Also, 80% PMP VO2 was less than VO2peak (P = 0.013). There were differences in RER at Tlim (P < 0.001, ES = 0.593) with values increasing with % PMP (1.15 s=0.07, 1.26 s=0.07, 1.36 s=0.10, 1.40 s=0.09, respectively). There were no differences across trials for HR at Tlim (~173 (12); P = 0.834, ES = 0.016) and HR was proportional to %PMP at 1 min, and 2 min. For flexor carpi ulnaris there was an increase in activation as exercise intensity increased (P < 0.001, ES = 0.245). There were a similar responses for biceps brachii and triceps brachii demonstrating an increase in activation with exercise intensity (P <0.001, ES = 0.137, P < 0.001, ES = 0.163, respectively). No differences for RPEL and RPECR were observed at Tlim. Discussion: There was a clear response of Tlim with intensity as expected for lower body exercise (Hill et al., 2002: Medicine and Science in Sports and Exercise, 34(4), 709-714). Despite differences in Tlim across exercise intensities VO2, HR and RPE were similar at exhaustion indicating a functional cardiorespiratory maximum had been reached. As indicated by the RER an increased activation of the anaerobic metabolism with greater exercise intensities (100% and 110%) is likely and therefore this may represent a greater anaerobic component at these two intensities. The increase in EMG activity with intensity could indicate an increase activity with an increase in exercise intensity. Conclusion: It is recommended that due to the combination of muscle activation, oxygen uptake and Tlim that an exercise intensity of 90% or 100% of PMP could be used for high intensity upper body exercise testing

The External Validity of a Novel Contract-Relax Stretching Technique on Knee Flexor Range of Motion

INTRODUCTION: Compromised joint range of motion (ROM) can negatively affect the capacity to perform activities of daily living in clinical populations. Recently, similar improvements in dorsiflexion ROM were reported following dynamometry-based contract-relax (CR) stretching and modified CR stretching technique (stretch-return-contract [SRC]) where the contraction phase was performed "off stretch." As neither the impact of SRC on other muscle groups nor the ecological validity of SRC performed in an applied environment has been tested, the acute effects of both techniques in dynamometry- (CR dyna and SRC dyna ) and field-based (CR field and SRC field ) environments were compared with the hamstring muscle group. METHODS: Seventeen participants performed each of the four stretching conditions on separate days in a randomized order. Before and after the stretches, knee extension ROM and passive knee flexor moment were recorded on an isokinetic dynamometer. RESULTS: Significant (P .05) in any measure was found between conditions. CONCLUSIONS: These data confirm the acute efficacy of the SRC technique in the hamstring muscle group and demonstrate its ecological validity in an applied environment in healthy participants. As the field-based SRC technique was performed without partner assistance, when compared with classical PNF it represents an equally effective and practical stretching paradigm to support athletic and clinical exercise prescription

Canadian Society For Exercise Physiology Position Stand on the Acute Effects of Muscle Stretching on Physical Performance, Range of Motion and Injury Incidence in Healthy Active Individuals

Muscle stretching in some form appears to be of greater benefit than cost (in terms of performance, ROM and injury outcomes) but the type of stretching chosen and the make-up of the stretch routine will depend on the context within which it is used. SS and PNF stretching are not recommended if prolonged (>60s total per individual muscle) stretching is employed within 5 min of an activity without subsequent dynamic activity (e.g. if prolonged stretching immediately precedes training or competition), unless the requirements for increases in ROM and/or decrease in (specifically) muscle injury outweigh the requirement for optimum physical performance. Injury reduction appears to require more than 5 min of total stretching of multiple task-related muscle groups. However, when an optimal pre-event warm-up with an appropriate duration of stretching is completed (i.e. initial aerobic activity, stretching component, task- or activity-specific dynamic activities) the benefits of SS and PNF stretching for increasing ROM and reducing muscle injury risk at least balance, or may outweigh, any possible cost of performance decrements. SS also appears to enhance performance in activities performed at long muscle lengths. DS may induce moderate performance enhancements and may be included in the stretching component to provide task-specific ROM increases and facilitation of dynamic SSC performance when performed soon before an activity, and/or when a full pre-activity routine is not completed; however there is no evidence as to whether it influences injury risk. Furthermore, while the literature examining the effect of stretching on physical performance is extensive, the literature examining injury risk is much smaller, and thus more research needs to investigate the effect of muscle stretching on injury risk

Stretching of active muscle elicits chronic changes in multiple strain risk factors

Introduction: The muscle stretch intensity imposed during 'flexibility' training influences the magnitude of joint range of motion (ROM) adaptation. Thus, stretching whilst the muscle is voluntarily activated was hypothesized to provide a greater stimulus than passive stretching. The effect of a 6-week program of stretch imposed on an isometrically-contracting muscle (i.e. qualitatively similar to isokinetic eccentric training) on muscle-tendon mechanics was therefore studied in 13 healthy human volunteers. Methods: Before and after the training program, dorsiflexion ROM, passive joint moment, and maximal isometric plantar flexor moment were recorded on an isokinetic dynamometer. Simultaneous real-time motion analysis and ultrasound imaging recorded gastrocnemius medialis muscle and Achilles tendon elongation. Training was performed twice weekly and consisted of five sets of 12 maximal isokinetic eccentric contractions at 10[degrees][middle dot]s-1. Results: Significant increases (P0.05), a significant increase in tendon stiffness (31.2%; P<0.01) and decrease in passive muscle stiffness (-14.6%; P<0.05) was observed. Conclusion: The substantial positive adaptation in multiple functional and physiological variables that are cited within the primary aetiology of muscle strain injury, including strength, ROM, muscle stiffness, and maximal energy storage, indicate that the stretching of active muscle might influence injury risk in addition to muscle function. The lack of change in muscle-tendon stiffness simultaneous with significant increases in tendon stiffness and decreases in passive muscle stiffness indicates that tissue-specific effects were elicited

Fair relationships and policies to support family day care educators’ mental health: a qualitative study

High quality child care is a population health investment that relies on the capacity of providers. The mental health and wellbeing of child care educators is fundamental to care quality and turnover, yet sector views on the relationship between working conditions and mental health and wellbeing are scarce. This paper examines child care educators\u27 and sector key informants\u27 perspectives on how working in family day care influences educator\u27s mental health and wellbeing

Acute effects of contract-relax (CR) stretch versus a modified CR technique

Purpose Contract–relax (CR) stretching increases range of motion (ROM) substantively, however its use in athletic environments is limited as the contractions performed in a highly stretched position require partner assistance, are often painful, and may induce muscle damage. Therefore, the acute effects of performing the contractions ‘off stretch’ in the anatomical position [stretch–return–contract (SRC)] were compared with traditional CR stretching in 14 healthy human volunteers. Methods Passive ankle joint moment and dorsiflexion ROM were recorded on an isokinetic dynamometer with electromyographic monitoring of the triceps surae, whilst simultaneous real-time motion analysis and ultrasound imaging recorded gastrocnemius medialis muscle and Achilles tendon elongation. The subjects then performed CR or SRC stretches (4 × 10-s stretches and 5-s contractions) randomly on separate days before reassessment. Results Significant increases in dorsiflexion ROM (4.1°– 4.0°; P 0.05). Conclusions Similar mechanical and neurological changes were observed between conditions, indicating that identical mechanisms underpin the ROM improvements. These data have important practical implications for the use of this stretching mode in athletic environments as performing the contractions ‘off stretch’ eliminates the pain response, reduces the risk of inducing muscle damage, and removes the need for partner assistance. Thus, it represents an equally effective, simpler, and yet potentially safer, stretching paradigm