Exercise as a countermeasure to human ageing

In less than 200 years, life expectancy in the United Kingdom has doubled from ~40 to ~80 years, a trend mirrored in most developed and now developing countries. The healthogenic effects of staying active across the lifespan are widely promoted, yet only 36% of men and 18% of women >75 years of age in England achieve the physical activity guidelines of 150 min/wk. Reduced functional ability as we age is caused by a natural weakening of physiological systems, exacerbated by physical inactivity. This talk will discuss benefits of, and barriers to, physical activity and exercise in older cohorts, with a focus on resistance training

Assessment of muscle activation capacity: methodological considerations of muscle mechanics and implications for testing

Muscle activation capacity assessment could be affected by the mechanical behaviour of the muscle, but this aspect has received little attention. Understanding the effect the muscle’s mechanical behaviour has on muscle activation capacity assessment can be paramount in achieving a better understanding of muscle function. The aim of the present Thesis was to examine the methodological implications of the mechanical behaviour of the muscle during muscle activation capacity assessment. Four studies were designed to examine the effect of the muscle-tendon unit on a) muscle activation capacity calculation methods and number of stimuli used, by manipulating quadriceps muscle length and consequently stiffness, b) stimulation intensity required and associated discomfort, by examining whether a lower than supramaximal stimulation intensity threshold, sufficient to stretch the muscle-tendon, exists, and c) the interplay between muscle mechanics and activation, by manipulating the testing position on the dynamometer, stabilisation and concurrent activation of remote muscles. Isometric knee extensions were used for all studies, and electrical stimuli was delivered to the muscle to quantify muscle activation capacity or induce muscular contractions by circumventing the voluntary neural drive. The results showed that a) altered muscle stiffness affects muscle activation values depending on the calculation method and number of stimuli used, suggesting caution to testing where muscle stiffness is likely to change, b) a lower stimulation intensity exists that can reduce subject discomfort while obtaining valid activation capacity results, widening the application of electrical muscle stimulation, and c) muscle activation must be considered in musculoskeletal models for more accurate predictions but the level of activation will ultimately depend on how stabilised the muscle is. Collectively, these results demonstrate the considerable effect muscle mechanics have on muscle activation capacity and that muscle strength assessment must take into account this aspect for more accurate inferences on muscle function

PREVIOUS BALLISTIC AND HEAVY CONDITIONING STIMULI CAN ACUTELY ENHANCE THROWING PERFORMANCE

The purpose of this study was to compare the effects of a ballistic and a heavy load conditioning stimulus on subsequent bench throw performance. Eleven male, competitive rugby players (mean ± SD: body mass 91.5 ± 9.6kg, height 1.79 ± 0.03 m) with at least two years of resistance training exercise performed two ballistic bench throws after warm up. Following a 10-min rest, they performed either a ballistic bench throw (BAL) or a heavy load bench press (HEAVY) conditioning stimulus. Subsequent to a 4-minute rest, they performed another two ballistic bench press throws. No significant differences were revealed for peak power, peak force, rate of force development and force at peak power for either conditioning stimulus. However, significant differences were revealed for bar displacement for the BAL group, and for peak velocity and velocity at peak power for both groups. The results suggest that a ballistic conditioning stimulus can induce post activation performance enhancement and it appears more sport specific in its results than a heavy load conditioning stimulu

Previous dynamic and ballistic conditioning contractions can enhance subsequent throwing performance (conference proceedings)

Previous muscle activity can potentiate subsequent muscle performance, a phenomenon known as post-activation potentiation (Tillin and Bishop, 2009, Sports Medicine, 39, 147-166). Although the effect of heavy load dynamic and plyometric conditioning contractions on enhancing subsequent explosive performance acutely has been examined (Esformes, Cameron and Bampouras, 2010, Journal of Strength and Conditioning Research, 24, 1911-1916), little information exists on using a ballistic activity as conditioning contraction

EXPLORING DIFFERENCES IN ELECTROMYOGRAPHY AND GROUND REACTION FORCES BETWEEN FRONT AND BACK SQUATS BEFORE AND AFTER A FATIGUING PROTOCOL

Limited research has been conducted to explore differences in biomechanical and physiological demands of the front and back squat, especially in response to fatigue where technique may be altered. This study investigated differences in electromyography and ground reaction forces during a 3-repetition maximum back and front squat before and after a fatiguing protocol in 30 males. Mean and peak activation of the semitendinosus was greater in the back squat than the front squat (p \u3c 0.05). There were no differences in quadricep activation between back and front squats. There were no differences in electromyography as a result of fatigue, however, force production decreased for back squats following fatigue (p \u3c 0.01). This research disputed the notion that front squats have a greater quadricep focus, however lends support to the hypothesis that quadricep activation equal to the back squat can be achieved with lighter absolute load in a front squat. The finding of lower ground reaction forces for the back squat following the fatiguing protocol in addition to no differences in electromyography between front and back squats indicates greater effects of the fatiguing protocol on back squat performance

Carrying shopping bags poses no additional fall risk to healthy older females as assessed by statistic and dynamic stability

Food shopping is an important aspect of maintaining independence and social interaction in older age (AgeUK, 2012, Food Shopping in Later Life). Carrying the shopping bags home, however, may pose higher fall risk. Carriage of UK-style shopping bag alters the body’s weight distribution by lowering the centre of gravity resulting in a more balanced static stance; however, when this stance is disturbed, it creates additional torsion which might make recovery difficult. The aim of the project, therefore, was to examine the effect of carrying shopping bags on static and dynamic postural stability in healthy older females aged over 65 years. Following institutional ethics approval, nine older females (aged 71 (s 5.9) years) performed both static and dynamic postural stability assessments carrying bags of varying loads and distributions (no bags, one 1.5-kg bag in each hand, one 3-kg bag in each hand, one 1.5-kg bag in preferred hand only, one 3-kg bag in preferred hand only; loads representing typical weight of essential shopping items) in a randomised order. For static postural stability assessment, participants stood quietly feet width apart on a force platform (AMTI, Massachusetts) for 30 s. Anteroposterior and mediolateral displacements, 95% ellipse area and sway velocity were calculated (BioAnalysis, Massachusetts). For dynamic postural stability, participants balanced on an uneven surface (Biodex, New York) for 30 s. Total anteroposterior and mediolateral displacements were calculated. Additionally, the load carried was quantified relative to handgrip strength (Takei Scientific Inst. Co. Ltd, Japan). A repeated measures analysis was used, and significance was set at P < 0.05. The heaviest load (3 kg in each hand, 6 kg in total) was 9.1% (range 7%–11%) of body mass. The heaviest load (3 kg in each hand) was 14.3% (range 9.8%– 22.8%) of handgrip strength. Neither static nor dynamic postural stability were affected by carrying shopping bags. The postural stability variables assessed have been previously shown to be related to fall risk (Fernie et al., 1982, Age and Ageing, 11, 11–16). The present findings suggest that despite the disturbance caused by the additional load, carrying shopping bags either in one hand only or in both hands does not increase the fall risk in older females, as seen from the similar static and dynamic postural stability scores across conditions. These results should help to alleviate concerns regarding safety of carrying shopping bags, thereby reducing social isolation, maintaining independence and increasing physical activity (Hornyak et al., 2013, Archives of Physical Medicine and Rehabilitation, 94, 2529–2534)

Ankle dorsiflexion range of motion asymmetry does not influence landing forces during a bilateral drop-landing

Ankle dorsiflexion range of motion (ROM) has a reported relationship (r = -0.31) with peak vertical ground reaction forces (vGRF) during landing activities, with higher peak vGRF produced among those with the greatest ROM deficit.2 The commonly reported inter-limb asymmetries in ankle dorsiflexion ROM among healthy populations5 and athletes3 are therefore, likely to influence the kinetic landing profile. However, the relationship between interlimb asymmetry in ankle dorsiflexion ROM and the loading strategy utilised during landings has not yet been investigated. The purpose of this investigation was to assess the relationship between asymmetries in ankle dorsiflexion ROM and kinetic variables associated with bilateral drop-landing performance

Restricted Unilateral Ankle Dorsiflexion Movement Increases Interlimb Vertical Force Asymmetries in Bilateral Bodyweight Squatting

The purpose of this study was to investigate the effect of unilateral restrictions in ankle-dorsiflexion range of motion (DF-ROM) on interlimb vertical ground reaction force (vGRF) asymmetries. Twenty healthy and physically active volunteers (age 23 ± 3 years; height 1.72 ± 0.1 m; mass 74.9 ± 20.3 kg) performed 3 barefoot bodyweight squats (control condition) and with a 10° custom-built forefoot wedge under the right foot to artificially imitate ankle DF-ROM restriction (wedge condition). Force data were used to calculate the mean asymmetry index score for the upper descent phase, lower descent phase, lower ascent phase, and upper ascent phase during the bilateral squat. Significant differences were found for comparisons for each phase between conditions, with effect sizes ranging between 0.7 and 1.1. Asymmetry index scores indicated that for all phases, the unrestricted limb in the wedge condition produced greater vGRF. Therefore, interlimb differences in ankle DF-ROM can cause interlimb asymmetries in vGRF during bilateral squatting. As such, athletes with asymmetrical squat mechanics should be screened for interlimb differences in ankle DF-ROM to ascertain whether it is a contributing factor

Upper limb muscle strength and knee frontal plane projection angle asymmetries in female water-polo players

Water-polo players frequently perform overhead throws that could result in shoulder imbalances. For overhead throws, execution of the ‘eggbeater kick’ (cyclical movement of the legs) is required to lift the body out of the water. Although a symmetrical action, inter-limb differences in task execution could lead to knee frontal plane projection (FPPA) differences. The present study examined imbalances shoulder and knee FPPA in female players. Eighteen competitive female field players (24.1 ± 5.5 years, 1.68 ± 0.06 m, 72.9 ± 13.3 kg) had their shoulder strength assessed in a shot-mimicking position with a portable dynamometer, standing and seated (isolating the shoulder contribution). Anterior: posterior and shooting: non-shooting shoulder comparison were made. Additionally, players performed a drop jump. Knee FPPA was recorded from digitising and comparing the frames just before landing and at stance phase. During standing, players exhibited higher shooting: non-shooting asymmetry (p = 0.032) in the anterior contraction direction, while during seated the shooting shoulder anterior: posterior asymmetry was higher (p = 0.032). Interlimb knee FPPA asymmetry was higher in the stance phase (p = 0.02). Despite the overhead throwing and egg-beater demands impacting differently on each limb, considerable asymmetries do not develop, suggesting the overall training requirements (e.g. swimming, resistance training) were sufficient to maintain the asymmetry within desirable limits

Validity and reliability of two field-based leg stiffness devices:Implications for practical use

Leg stiffness is an important performance determinant in several sporting activities. This study evaluated the criterion-related validity and reliability of 2 field-based leg stiffness devices, Optojump Next® (Optojump) and Myotest Pro® (Myotest) in different testing approaches. Thirty-four males performed, on 2 separate sessions, 3 trials of 7 maximal hops, synchronously recorded from a force platform (FP), Optojump and Myotest. Validity (Pearson's correlation coefficient, r; relative mean bias; 95% limits of agreement, 95%LoA) and reliability (coefficient of variation, CV; intraclass correlation coefficient, ICC; standard error of measurement, SEM) were calculated for first attempt, maximal attempt, and average across 3 trials. For all 3 methods, Optojump correlated highly to the FP (range r =.98-.99) with small bias (range 0.91-0.92, 95%LoA 0.86-0.98). Myotest demonstrated high correlation to FP (range r =.81-.86) with larger bias (range 1.92-1.93, 95%LoA 1.63-2.23). Optojump yielded a low CV (range 5.9% to 6.8%), high ICC (range 0.82-0.86), and SEM ranging 1.8-2.1 kN/m. Myotest had a larger CV (range 8.9% to 13.0%), moderate ICC (range 0.64-0.79), and SEM ranging from 6.3 to 8.9 kN/m. The findings present important information for these devices and support the use of a time-efficient single trial to assess leg stiffness in the field