High-fat diet effects on contractile performance of isolated mouse soleus and extensor digitorum longus when supplemented with high dose vitamin D.

Evidence suggests vitamin D3 (VD) supplementation can reduce accumulation of adipose tissue and inflammation and promote myogenesis in obese individuals, and thus could mitigate obesity-induced reductions in skeletal muscle (SkM) contractility. However, this is yet to be directly investigated. This study, using the work-loop technique, examined effects of VD (cholecalciferol) supplementation on isolated SkM contractility. Female mice (n = 37) consumed standard low-fat diet (SLD) or high-fat diet (HFD), with or without VD (20,000 IU/kg-1 ) for 12 weeks. Soleus and EDL (n = 8-10 per muscle per group) were isolated and absolute and normalized (to muscle size and body mass) isometric force and power output (PO) were measured, and fatigue resistance determined. Absolute and normalized isometric force and PO of soleus were unaffected by diet (P > 0.087). However, PO normalized to body mass was reduced in HFD groups (P < 0.001). Isometric force of extensor digitorum longus (EDL) was unaffected by diet (P > 0.588). HFD reduced EDL isometric stress (P = 0.048) and absolute and normalized PO (P < 0.031), but there was no effect of VD (P > 0.493). Cumulative work during fatiguing contractions was lower in HFD groups (P < 0.043), but rate of fatigue was unaffected (P > 0.060). This study uniquely demonstrated that high-dose VD had limited effects on SkM contractility and did not offset demonstrated adverse effects of HFD. However, small and moderate effect sizes suggest improvement in EDL muscle performance and animal morphology in HFD VD groups. Given effect sizes observed, coupled with proposed inverted U-shaped dose-effect curve, future investigations are needed to determine dose/duration specific responses to VD, which may culminate in improved function of HFD SkM.

Effect of high-fat diet on isometric, concentric and eccentric contractile performance of skeletal muscle isolated from female CD-1 mice.

Despite evidence inferring muscle and contractile mode-specific effects of high-fat diet (HFD), no study has yet considered the impact of HFD directly on eccentric muscle function. The present work uniquely examined the effect of 20-week HFD on the isometric, concentric and eccentric muscle function of isolated mouse soleus (SOL) and extensor digitorum longus (EDL) muscles. CD-1 female mice were randomly split into a control (n = 16) or HFD (n = 17) group and for 20 weeks consumed standard lab chow or HFD. Following this period, SOL and EDL muscles were isolated and assessments of maximal isometric force and concentric work loop (WL) power were performed. Each muscle was then subjected to either multiple concentric or eccentric WL activations. Post-fatigue recovery, as an indicator of incurred damage, was measured via assessment of concentric WL power. In the EDL, absolute concentric power and concentric power normalised to muscle mass were reduced in the HFD group (P < 0.038). HFD resulted in faster concentric fatigue and reduced eccentric activity-induced muscle damage (P < 0.05). For the SOL, maximal isometric force was increased, and maximal eccentric power normalised to muscle mass and concentric fatigue were reduced in the HFD group (P < 0.05). HFD effects on eccentric muscle function are muscle-specific and have little relationship with changes in isometric or concentric function. HFD has the potential to negatively affect the intrinsic concentric and eccentric power-producing capacity of skeletal muscle, but a lack of a within-muscle uniform response indicates disparate mechanisms of action which require further investigation.

The effects of muscle starting length on work loop power output of isolated mouse soleus and extensor digitorum longus muscle.

Force-length relationships derived from isometric activations may not directly apply to muscle force production during dynamic contractions. As such, different muscle starting lengths between isometric and dynamic conditions could be required to achieve maximal force and power. Therefore, this study examined the effects of starting length [±5-10% of length corresponding to maximal twitch force (L0)] on work loop (WL) power output (PO), across a range of cycle frequencies, of the soleus (SOL) and extensor digitorum longus muscle (EDL; N=8-10) isolated from ∼8 week old C57 mice. Furthermore, passive work was examined at a fixed cycle frequency to determine the association of passive work and active net work. Starting length affected maximal WL PO of the SOL and EDL across evaluated cycle frequencies (P<0.030, ηp2>0.494). For the SOL, PO produced at -5% L0 was greater than that at most starting lengths (P<0.015, Cohen's d>0.6), except -10% L0 (P=0.135, d<0.4). However, PO produced at -10% L0 versus L0 did not differ (P=0.138, d=0.35-0.49), indicating -5% L0 is optimal for maximal SOL WL PO. For the EDL, WL PO produced at -10% L0 was lower than that at most starting lengths (P<0.032, d>1.08), except versus -5% L0 (P=0.124, d<0.97). PO produced at other starting lengths did not differ (P>0.163, d<1.04). For the SOL, higher passive work was associated with reduced PO (Spearman's r=0.709, P<0.001), but no relationship was observed between passive work and PO of the EDL (Pearson's r=0.191, r2=0.04, P=0.184). This study suggests that starting length should be optimised for both static and dynamic contractions and confirms that the force-length curve during dynamic contractions is muscle specific.

Shuttle Time for Seniors: The Impact of 8-Week Structured Badminton Training on Markers of Healthy Aging and Evaluation of Lived Experiences-A Quasi-Experimental Study.

BACKGROUND/OBJECTIVES: Engagement in sport offers the potential for improved physical and psychological well-being and has been shown to be beneficial for promoting healthy aging. Opportunities for older adults to (re)engage with sport are limited by a paucity of age-appropriate introductory sports intervention programs. As such, the study evaluated the efficacy of a newly designed 8-week badminton training program (Shuttle Time for Seniors) on markers of healthy aging and the lived experiences of participation. METHODS: Forty-three older adults assigned to a control (N = 20) or intervention group (N = 23) completed pre-post assessment of physical and cognitive function, self-efficacy for exercise, and well-being. Focus groups were conducted for program evaluation and to understand barriers and enablers to sustained participation. RESULTS: Those in the intervention group increased upper body strength, aerobic fitness, coincidence anticipation time, and self-efficacy for exercise. Objectively improved physical and cognitive functions were corroborated by perceived benefits indicated in thematic analysis. Shuttle Time for Seniors was perceived as appropriate for the population, where the age-appropriate opportunity to participate with likeminded people of similar ability was a primary motivator to engagement. Despite willingness to continue playing, lack of badminton infrastructure was a primary barrier to continued engagement. CONCLUSION: Shuttle Time for Seniors offered an important opportunity for older adults to (re)engage with badminton, where the physical and psychosocial benefits of group-based badminton improved facets important to healthy aging. Significance/Implications: Age-appropriate introductory intervention programs provide opportunity for older adults to (re)engage with sport. However, important barriers to long-term engagement need to be addressed from a whole systems perspective.

Force-Time Characteristics of Repeated Bouts of Depth Jumps and the Effects of Compression Garments.

No studies have reported ground reaction force (GRF) profiles of the repeated depth jump (DJ) protocols commonly used to study exercise-induced muscle damage. Furthermore, while compression garments (CG) may accelerate recovery from exercise-induced muscle damage, any effects on the repeated bout effect are unknown. Therefore, we investigated the GRF profiles of 2 repeated bouts of damage-inducing DJs and the effects of wearing CG for recovery. Nonresistance-trained males randomly received CG (n = 9) or placebo (n = 8) for 72 hours recovery, following 20 × 20 m sprints and 10 × 10 DJs from 0.6 m. Exercise was repeated after 14 days. Using a 3-way (set × bout × group) design, changes in GRF were assessed with analysis of variance and statistical parametric mapping. Jump height, reactive strength, peak, and mean propulsive forces declined between sets (P < .001). Vertical stiffness, contact time, force at zero velocity, and propulsive duration increased (P < .05). According to statistical parametric mapping, braking (17%-25% of the movement) and propulsive forces (58%-81%) declined (P < .05). During the repeated bout, peak propulsive force and duration increased (P < .05), while mean propulsive force (P < .05) and GRF from 59% to 73% declined (P < .001). A repeated bout of DJs differed in propulsive GRF, without changes to the eccentric phase, or effects from CG.

The effect of medical grade compression garments on the repeated-bout effect in non-resistance-trained men.

NEW FINDINGS: What is the central question of this study? What are the effects of compression garments on recovery from unaccustomed damaging exercise and subsequent protective adaptations? What is the main finding and its importance? Compression did not influence recovery, but was associated with blunted protective adaptations for isokinetic performance, which were completely absent at high velocities. Based on these findings, the use of compression garments for recovery would not be recommended following unaccustomed exercise, particularly if the maintenance of high-velocity performance following exercise-induced muscle damage is desirable. ABSTRACT: Whilst compression garments (CG) may enhance recovery from exercise-induced muscle damage (EIMD), many recovery strategies can attenuate adaptative responses. Therefore, the effects of CG on recovery from EIMD, and the rapid protective adaptations known as the repeated bout effect (RBE) were investigated. Thirty-four non-resistance-trained males (18-45 years) randomly received class II medical-grade CG or placebo for 72 h following eccentrically-focused lower-body exercise, in a double-blind, randomised controlled trial. Indices of EIMD were assessed at baseline, 0, 24, 48 and 72 h post-exercise, before exercise and testing were repeated after 14 days. Results were analysed using a three-way (time × condition × bout) linear mixed-effects model. Exercise impaired isometric and isokinetic strength, with soreness and thigh circumference elevated for 72 h (P < 0.001). Compression did not enhance recovery (P > 0.05), despite small to moderate effect sizes (ES, reported alongside 90% confidence intervals) for isokinetic strength (ES from 0.2 [-0.41, 0.82] to 0.65 [0.03, 1.28]). All variables recovered faster after the repeated bout (P < 0.005). However, RBE for peak isokinetic force was impaired in CG at 60° s-1 (group × bout interaction: χ2  = 4.24, P = 0.0395; ES = -0.56 [-1.18, 0.07]) and completely absent at 120° s-1 (χ2  = 16.2, P < 0.001, ES = -0.96 [-1.61, -0.32]) and 180° s-1 (χ2  = 10.4, P = 0.001, ES = -0.72 [-1.35, -0.09]). Compression blunted RBE at higher isokinetic velocities without improving recovery in non-resistance-trained males, potentially contraindicating their use following unaccustomed exercise in this population.

Can animals tune tissue mechanics in response to changing environments caused by anthropogenic impacts?

Anthropogenic climate change and pollution are impacting environments across the globe. This Review summarises the potential impact of such anthropogenic effects on animal tissue mechanics, given the consequences for animal locomotor performance and behaviour. More specifically, in light of current literature, this Review focuses on evaluating the acute and chronic effects of temperature on the mechanical function of muscle tissues. For ectotherms, maximal muscle performance typically occurs at temperatures approximating the natural environment of the species. However, species vary in their ability to acclimate to chronic changes in temperature, which is likely to have longer-term effects on species range. Some species undergo periods of dormancy to avoid extreme temperature or drought. Whilst the skeletal muscle of such species generally appears to be adapted to minimise muscle atrophy and maintain performance for emergence from dormancy, the increased occurrence of extreme climatic conditions may reduce the survival of individuals in such environments. This Review also considers the likely impact of anthropogenic pollutants, such as hormones and heavy metals, on animal tissue mechanics, noting the relative paucity of literature directly investigating this key area. Future work needs to determine the direct effects of anthropogenic environmental changes on animal tissues and related changes in locomotor performance and behaviour, including accounting for currently unknown interactions between environmental factors, e.g. temperature and pollutants.

Effect of stimulation frequency on force, power and fatigue of isolated mouse extensor digitorum longus muscle.

This study examined the effect of stimulation frequency (140, 200, 230 and 260 Hz) on isometric force, work loop (WL) power and the fatigue resistance of extensor digitorum longus (EDL) muscle (n=32), isolated from 8- to 10-week-old CD-1 female mice. Stimulation frequency had significant effects on isometric properties of isolated mouse EDL, whereby increasing stimulation frequency evoked increased isometric force, quicker activation and prolonged relaxation (P<0.047) up to 230 Hz and above; thereafter, force and activation did not differ (P>0.137). Increasing stimulation frequency increased maximal WL power output (P<0.001; 140 Hz, 71.3±3.5; 200 Hz, 105.4±4.1; 230 Hz, 115.5±4.1; 260 Hz, 121.1±4.1 W kg-1), but resulted in significantly quicker rates of fatigue during consecutive WLs (P<0.004). WL shapes indicate impaired muscle relaxation at the end of shortening and subsequent increased negative work appeared to contribute to fatigue at 230 and 260 Hz, but not at lower stimulation frequencies. Cumulative work was unaffected by stimulation frequency, except at the start of the fatigue protocol, where 230 and 260 Hz produced more work than 140 Hz (P<0.039). We demonstrate that stimulation frequency affects force, power and fatigue, but these effects are not uniform between different assessments of contractile performance. Therefore, future work examining the contractile properties of isolated skeletal muscle should consider increasing the stimulation frequency beyond that needed for maximal force when examining maximal power but should utilise a sub-maximal stimulation frequency for fatigue assessments to avoid a high degree of negative work atypical of in vivo function.

High-fat diet affects measures of skeletal muscle contractile performance in a temperature-specific manner but does not influence regional thermal sensitivity.

The present study examined whether high-fat diet (HFD) consumption for 20 weeks had a temperature-specific effect on the contractile performance and regional thermal sensitivity of isolated mouse soleus and diaphragm muscle. Four-week-old female CD-1 mice were randomly selected to consume either a standard laboratory diet or a standard laboratory diet in conjunction with a HFD for 20 weeks. Peripheral soleus and core diaphragm were isolated from each animal and maximal isometric force and work loop power were assessed at 20, 28, 35 and 40°C. Increasing temperature to 35°C resulted in greater isometric stress, lower activation and relaxation time, and higher work loop power in both muscles. A further increase in temperature to 40°C did not affect isometric force but increased work loop power output of the soleus. Conversely, isometric force of the diaphragm was reduced and work loop power maintained when temperature was increased to 40°C. HFD consumption resulted in greater isometric force and absolute work loop power of the soleus and reduced isometric stress of the diaphragm, effects that were less apparent at lower temperatures. When the relationship between temperature and each measure of contractile function was examined by linear regression, there was no difference in slope between the control or HFD groups for either the soleus or diaphragm. These results indicate that whilst contractile function initially increases with temperature, the temperature to elicit maximal performance is muscle and contractile mode specific. Furthermore, HFD effects on contractile function are temperature specific, but HFD does not influence the relationship between temperature and performance.

The influence of angle-specific torque of the knee flexors and extensors on the angle-specific dynamic control ratio in professional female soccer players.

The purpose of this study was to assess whether dynamic torque ratios (DCR) from isokinetic strength assessments of eccentric knee flexors (eccKF) and concentric knee extensors (conKE) display differences when stratified into specific angle-specific DCR (DCRAST) groups. Fifty-two professional female soccer players (age 21.30 ± 4.44 years; height 166.56 ± 5.17 cm; mass 61.55 ± 5.73 kg) from the English Women's Super League completed strength assessments of both lower limbs on an isokinetic dynamometer at 60°âˆ™s-1. Angle-specific torque (AST) were used to calculate DCRAST to create sub-groups using clustering algorithms. The results identified for the dominant side that the Medium DCRAST group elicited significantly higher conKE AST when compared to Low and High DCRAST groups at increased knee extension (P ≤ 0.05). For the non-dominant side, the High DCRAST group had significantly higher and lower eccKF and conKE AST compared to the Low DCRAST group at increased knee extension (P ≤ 0.05). This study highlights that the inclusion of AST data may subsequently help practitioners to prescribe exercise that promotes strength increases at targeted joint angles. In turn, these approaches can be used to help reduce injury risk, identify rehabilitation responses and help inform return to play.

Identifying actual and perceived motor competence based profiles among children.

This study aimed to develop motor competence (MC) profiles in children based on their actual and perceived MC, and to investigate differences in physical activity (PA) behaviour and motivation towards PA between profiles. Two hundred and sixteen British children (7-10 years) took part in this study. Perceived motor competence (PMC) was assessed using the pictorial scale of movement competence. MC was assessed using process-oriented and product-oriented measures. A validated questionnaire assessed motivation towards PA and an objective measure of PA was employed. K-means cluster analysis was used to create profiles. Differences in PA and motivation towards PA were examined using ANCOVAs. Four groups of divergent and convergent levels were identified based on the contribution of either product or process MC with PMC. Motivation towards PA differed by profiles that included actual-process and PMC. Children with high actual process and high PMC had significantly higher levels of autonomous motivation than children with high actual process but low PMC. No significant differences were found between PA levels and profiles. Developing the quality and execution of actual motor competence (AMC) and PMC is key to stimulate motivation towards PA. Furthermore, maintaining AMC and PMC simultaneously may be imperative to children's future PA behaviour.

The Effects of Physical Fitness on Postactivation Potentiation in Professional Soccer Athletes.

ABSTRACT: Guerra, MA Jr, Caldas, LA, Souza, HL, Tallis, J, Duncan, MJ, and Guimarães-Ferreira, L. The effects of physical fitness on postactivation potentiation in professional soccer athletes. J Strength Cond Res 36(6): 1643-1647, 2022-To investigate the relationship of the response to postactivation potentiation (PAP) with scores of physical fitness. Twenty-four professional male soccer players undertook tests of agility, muscular power, aerobic capacity, and body composition. Conditioning activities (CAs) were performed consisting of plyometrics exercises and sprints with sled towing. In the first and second sessions, body composition, agility, power, and aerobic capacity were assessed. At the third session, countermovement jumps (CMJ) were performed with 1, 3, and 5 minutes after the execution of the CA. Significant differences were found for CMJ height 1, 3, and 5 minutes after the CA compared with baseline values (3.58, 5.10, 5.48%, respectively). There was a significant positive correlation between the level of general physical fitness and PAP (CMJ height increase) 5 minutes after (r = 0.73). When the athletes were divided into groups with higher and lower physical fitness, the CA caused a significant increase in CMJ height in both groups, but a significant difference (p < 0.05) was observed at all times after PAP induction, with better performance in higher versus lower fitness level. The results suggest that plyometrics exercises associated with sled towing sprints as a CA result in an increase in CMJ performance in athletes and that physical fitness directly influences the PAP occurrence, with higher fit players demonstrating an enhanced PAP response.

A High-Fat Diet Aggravates the Age-Related Decline in Skeletal Muscle Structure and Function.

The age-related decline in muscle function is aggravated by a high-fat diet (HFD)-induced increase in fat mass. The hypothesis is that an HFD leads to a faster accumulation of intramyocellular lipids (IMCL) and an earlier onset of muscle dysfunction in old than in young-adult individuals. The IMCL accumulation is attenuated in young-adult organisms by an elevated oxidative capacity. Methionine restriction enhances mitochondrial biogenesis and is promising to combat obesity across the ages.

The influence of COVID-19 measures in the United Kingdom on physical activity levels, perceived physical function and mood in older adults: A survey-based observational study.

In March 2020, the spreading Coronavirus (COVID-19) prompted the United Kingdom government to introduce a societal shutdown, accompanied by self-isolation and social-distancing measures to reduce virus transmission. In doing so, opportunities for physical activity were likely reduced, potentially causing detrimental effects to older adults. Therefore, the present study investigated the influence of the initial six weeks of lockdown on physical activity levels, perceived physical function and mood in older adults. A cross-sectional, mixed-methods, observational study was conducted using self-administered, fortnightly online surveys throughout the UK between 21st March-4 May 2020. A total of 117 participants (52 males [age: 76 ± 4 years] and 65 females [age: 76 ± 4 years]) completed all surveys. Despite lockdown restrictions, this group of older adults maintained their pre-lockdown physical activity levels, but also increased their self-reported sedentary time. Subsequently, perception of physical function was maintained across lockdown. With regards to mood; the only strong evidence for an increase in depression was for males (ps = 95.35%; >0.3 AU), although self-reported levels of depression were similar between sexes at week six. Given the link between sedentary behaviour and negative health outcomes in older adults, strategies to reduce sedentariness during the COVID-19 pandemic are required.

The prevalence and practices of caffeine use as an ergogenic aid in English professional soccer.

The ergogenic properties of caffeine are well established, with evidence supporting beneficial effects for physical and technical elements of performance required for successful soccer match play. Despite this, recommended caffeine practices for professional soccer have not been established. Therefore, the present study aimed to evaluate the use and behaviours surrounding caffeine use in elite English soccer clubs. Representatives of 36 clubs from the top four tiers of English professional football (40%) completed an online survey that sought to determine if, when, how and why caffeine was prescribed to players as a means of improving sports performance. Of the clubs sampled, 97% indicated that caffeine is provided to players as a means of improving performance. Caffeine is most commonly administered prior to (> 94%) and during a game (> 48%), with frequency uninfluenced by time of matches. There was a broad range and lack of consistency in the timing, dose and mode of caffeine administration, but doses were typically low. Evidence from the present study indicate a translational gap between science and practice, highlighting a need for future work to better understand how caffeine consumption can be optimised with respect to the specific demands and constraints in professional soccer.

Age-related changes in isolated mouse skeletal muscle function are dependent on sex, muscle, and contractility mode.

The present study aimed to simultaneously examine the age-related, muscle-specific, sex-specific, and contractile mode-specific changes in isolated mouse skeletal muscle function and morphology across multiple ages. Measurements of mammalian muscle morphology, isometric force and stress (force/cross-sectional area), absolute and normalized (power/muscle mass) work-loop power across a range of contractile velocities, fatigue resistance, and myosin heavy chain (MHC) isoform concentration were measured in 232 isolated mouse (CD-1) soleus, extensor digitorum longus (EDL), and diaphragm from male and female animals aged 3, 10, 30, 52, and 78 wk. Aging resulted in increased body mass and increased soleus and EDL muscle mass, with atrophy only present for female EDL by 78 wk despite no change in MHC isoform concentration. Absolute force and power output increased up to 52 wk and to a higher level for males. A 23-36% loss of isometric stress exceeded the 14-27% loss of power normalized to muscle mass between 10 wk and 52 wk, although the loss of normalized power between 52 and 78 wk continued without further changes in stress (P > 0.23). Males had lower power normalized to muscle mass than females by 78 wk, with the greatest decline observed for male soleus. Aging did not cause a shift toward slower contractile characteristics, with reduced fatigue resistance observed in male EDL and female diaphragm. Our findings show that the loss of muscle quality precedes the loss of absolute performance as CD-1 mice age, with the greatest effect seen in male soleus, and in most instances without muscle atrophy or an alteration in MHC isoforms.

The impact of a high-fat diet in mice is dependent on duration and age, and differs between muscles.

Prolonged high-fat diets (HFDs) can cause intramyocellular lipid (IMCL) accumulation that may negatively affect muscle function. We investigated the duration of a HFD required to instigate these changes, and whether the effects are muscle specific and aggravated in older age. Muscle morphology was determined in the soleus, extensor digitorum longus (EDL) and diaphragm muscles of female CD-1 mice from 5 groups: young fed a HFD for 8 weeks (YS-HFD, n=16), young fed a HFD for 16 weeks (YL-HFD, n=28) and young control (Y-Con, n=28). The young animals were 20 weeks old at the end of the experiment. Old (70 weeks) female CD-1 mice received either a normal diet (O-Con, n=30) or a HFD for 9 weeks (OS-HFD, n=30). Body mass, body mass index and intramyocellular lipid (IMCL) content increased in OS-HFD (P≤0.003). In the young mice, this increase was seen in YL-HFD and not YS-HFD (P≤0.006). The soleus and diaphragm fibre cross-sectional area (FCSA) in YL-HFD was larger than that in Y-Con (P≤0.004) while OS-HFD had a larger soleus FCSA compared with that of O-Con after only 9 weeks on a HFD (P<0.001). The FCSA of the EDL muscle did not differ significantly between groups. The oxidative capacity of fibres increased in young mice only, irrespective of HFD duration (P<0.001). High-fat diet-induced morphological changes occurred earlier in the old animals than in the young, and adaptations to HFD were muscle specific, with the EDL being least responsive.

Age-related degeneration of lumbar muscle morphology in healthy younger versus older men.

AIM: The aim of this study was to evaluate age-related changes in lumbar paravertebral muscle (LPM) morphology in healthy younger and older adult men. METHODS: T2-weighted axial MRI of the lumbar spine were obtained for 12 healthy older (67.3 ± 6.0 years) and younger (24.7 ± 3.1 years) men. Normalised muscle volume (NMV) and muscle fat infiltrate (MFI) were determined bilaterally for the psoas (PS), quadratus lumborum (QL), erector spinae (ES) and multifidus (MF). MANOVA was used to compare NMV and MFI between age groups. Follow-up ANOVA compared NMV and MFI for each muscle between age groups, with physical activity (PA) as a covariate. Stepwise regression was used to explore the association between muscle morphology. RESULTS: NMV of the ES and QL were significantly lower in the older group (OG) (p = 0.040 and p < 0.001, respectively). MFI across all muscles was significantly greater in the OG (p < 0.001). PA did not moderate the relationship between aging and muscle degeneration. Non-dominant handgrip strength was associated with NMV (p = 0.003). CONCLUSIONS: Age-related atrophy is muscle specific in the lumbar spine; changes in lumbar musculature is independent of PA, handgrip strength may reflect morphological changes in the postural muscles with age. This study supports establishing effective targeted exercise interventions in the lumbar musculature.

Cross-validation of Actigraph derived accelerometer cut-points for assessment of sedentary behaviour and physical activity in children aged 8-11 years.

AIM: To cross-validate previously calibrated Actigraph cut-points in children. METHODS: Twenty-eight children (50% boys) aged between 8 and 11 years of age (9.4 ± 1.4 years) performed a series of 5 minute bouts of activity reflective of different levels of PA from sedentary behaviour (SB) to moderate to vigorous physical activity (MVPA); V˙ O2 was assessed using breath-by-breath indirect calorimetry, and activity was assessed using Actigraph accelerometers worn on the hip and non-dominant wrist. The V˙ O2 values were then converted into age-specific METs (measured METs) and coded as SB, light PA and MVPA. Accelerometer data were analysed using previously calibrated cut-points at different epochs, that is 5, 15, 30 and 60 seconds. RESULTS: Receiver operating characteristic (ROC) curve analysis indicated that there was excellent discrimination of SB using the Evenson et al (15 seconds), Romanzini (15 seconds), Treuth et al (30 seconds), Freedson et al (60 seconds), Treuth et al (60 seconds) and Troiano et al (60 seconds) cut-points. ROC analysis indicated poor discrimination for LPA irrespective of the cut-points used. Good discrimination of MVPA was evident for all existing cut-points using a 60-second epoch. CONCLUSION: There is considerable variation in the performance of existing cut-points for assessment of SB, LPA and MPA in children.

Examining accelerometer validity for estimating physical activity in pre-schoolers during free-living activity.

The present study examined the efficacy of accelerometers for the assessment of free play physical activity (PA) in pre-school-aged children with consideration of epoch length and wear location. Following ethics approval, parental informed consent, and child assent, 66 pre-schoolers aged 3-4 years (30 females and 36 males) wore an accelerometer (ActiGraph GT3X; sampling at 100 Hz) on their non-dominant wrist and their right hip during 1 hour of free play. Concurrently, direct observation, using the OSRAC-P, was used to determine sedentary behavior (SB), light (LPA), or moderate-to-vigorous (MVPA) intensity PA. For the ActiGraph, vertical axis counts and summed vector magnitude (VM) for hip, and VM for wrist, were downloaded using 5-, 10-, 15-, and 30-second epoch lengths. Accelerometer counts were averaged over each 30 seconds to match the observation periods. Receiver operating curve analysis was used to evaluate the ability of the ActiGraph to predict SB, LPA, and MVPA. SB and MVPA obtained from wrist- and hip-worn accelerometers demonstrated fair agreement with direct observation (AUC => 0.7). LPA determined by accelerometer had poor agreement with observed LPA, for both the hip and wrist placement (AUC = 0.53-0.56), with weak levels of specificity (0.34-0.43), although sensitivity was fair (0.74-0.84). This study is the first to examine accelerometer validity, considering wear location and epoch in pre-schoolers during free play, and suggests that the ActiGraph is a fair measure for SB and MVPA in pre-school children. Neither placement performed predominantly better irrespective of epochs or used count data (vertical axis, VM).