Musculoskeletal Proportionality, Biomechanical Considerations and Their Contribution to Movement in Adults and Children.

The musculoskeletal system grows greatly throughout maturation. When trying to explain differences in strength, power and movement patterns between adults and children many pediatric exercise scientists will assume that this growth is proportional in all dimensions and structures. This article examines the evidence underpinning these assumptions, and considers how changes in fascicle, muscle, tendon and joint proportions may contribute to maturation-induced changes in physical performance. There are only a small number of studies to draw upon, but they consistently indicate that 1) growth changes the functional design of muscles, so that they become better at producing large forces at slow speeds but less able to achieve large length changes or high velocities; 2) the skeleton appears to grow somewhat proportionally prior to puberty, but this changes throughout adolescence, meaning the moment arm about which the muscle acts does not remain proportional to muscle length or the external moment arm about which joint work acts on the external world. In combination these results show that external measures of whole body or joint performance do not reflect the actual internal muscle function similarly in children and adults. Since our purpose should be to explain and not just describe maturation-induced changes in performance, greater efforts are needed to understand the internal "engine" driving our movement. This necessitates more detailed, longitudinal and dynamically loaded studies of the structure and function of the muscles and their interaction with the skeleton throughout maturation

Biomechanics and Exercise

Children develop lower levels of muscle force, and at slower rates, than adults. Whilst strength training in children is expected to reduce this differential, a synchronous adaptation in the tendon must be achieved to ensure forces continue to be transmitted to the skeleton with efficiency whilst minimizing the risk of strain-related tendon injury. We hypothesized that resistance training (RT) would alter tendon mechanical properties in children concomitantly with changes in force production characteristics. Twenty prepubertal children (8.9 ± 0.3 years) were equally divided into control (non-training) and experimental (training) groups. The training group completed a 10-week RT intervention consisting of 2-3 sets of 8-15 plantar flexion contractions performed twice-weekly on a recumbent calf raise machine. Achilles tendon properties (cross-sectional area, elongation, stress, strain, stiffness and Young’s modulus), electromechanical delay (EMD; time between the onset of muscle activity and force), rate of force development (RFD; slope of the force-time curve) and rate of EMG increase (REI; slope of the EMG-time curve) were measured before and after RT. Tendon stiffness and Young’s modulus increased significantly after RT in the experimental group only (~29% and ~25%, respectively); all other tendon properties were not significantly altered, although there were mean decreases in both peak tendon strain and strain at a given force level (14% and 24%, respectively (n.s)) which may have implications for tendon injury risk and muscle fiber mechanics. A ~13% decrease in EMD was found after RT for the experimental group which paralleled the increase in tendon stiffness (r = -0.59), however RFD and REI were unchanged. The present data show that the Achilles tendon adapts to RT in prepubertal children and is paralleled by a change in EMD, although the magnitude of this change did not appear to be sufficient to influence RFD. These findings are of potential importance within the context of the efficiency and execution of movement

Commentary on child-adult differences in muscle activation - A review

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Sagittal plane joint kinetics during stair ascent in patients with peripheral arterial disease and intermittent claudication

Stair negotiation poses a substantial physical demand on the musculoskeletal system and this challenging task can place individuals at risk of falls. Peripheral arterial disease (PAD) can cause intermittent claudication (IC) pain in the calf and results in altered gait mechanics during level walking. However, whether those with PAD-IC adopt alternate strategies to climb stairs is unknown. Twelve participants with PAD-IC (six bilateral and six unilateral) and 10 healthy controls were recruited and instructed to ascend a five-step staircase whilst 3D kinematic data of the lower-limbs were recorded synchronously with kinetic data from force plates embedded into the staircase on steps two and three. Limbs from the unilateral group and both limbs from the bilateral claudicants were categorised as claudicating (N = 18), asymptomatic (N = 6) and control (N = 10). Claudicants walked more slowly than healthy controls (trend; P = < 0.066). Both claudicating- and asymptomatic-limb groups had reduced propulsive GRF (P = 0.025 and P = 0.002, respectively) and vertical GRF (P = 0.005 and P = 0.001, respectively) compared to controls. The claudicating-limb group had a reduced knee extensor moment during forward continuance (P = 0.060), ankle angular velocity at peak moment (P = 0.039) and ankle power generation (P = 0.055) compared to the controls. The slower gait speed, irrespective of laterality of symptoms, indicates functional capacity was determined by the limitations of the claudicating limb. Reduced ankle power generation and angular velocity (despite adequate plantarflexor moment) implies velocity-dependent limitations existed in the calf. The lack of notable compensatory strategies indicates reliance on an impaired muscle group to accomplish this potentially hazardous task, highlighting the importance of maintaining plantarflexor strength and power in those with PAD-IC

Dynamic muscle quality of the plantar flexors is impaired in claudicant patients with peripheral arterial disease and associated with poorer walking endurance

Objectives: Peripheral arterial disease and intermittent claudication (PAD-IC) negatively affects physical activity and function. There is evidence for plantarflexor muscle dysfunction and weakness, however, the extent to which this dysfunction can be attributed to reduced muscle size and/or quality is not yet known. This study investigated whether in vivo plantarflexor muscle quality during static and dynamic contractions are altered by PAD-IC and whether such changes are associated with impaired walking endurance (according to initial and absolute claudication distances). Methods: A total of 22 participants were recruited, consisting of 10 healthy controls and 12 claudicants with occlusion of the superficial femoral artery (seven unilateral and five bilateral). Muscle quality of the combined gastrocnemius muscles during static contractions was calculated by normalising the estimated maximal potential muscle force to the physiological cross-sectional area of both lateral and medial gastrocnemius. Muscle quality during dynamic contractions of the combined plantarflexor muscles was calculated as the ratio of peak voluntary concentric plantarflexor power and the summed volume of lateral and medial gastrocnemius. Results: Dynamic muscle quality was 24% lower in both the claudicating-limb and asymptomatic-limb groups compared to controls (P=.017 and P=.023). The differences were most apparent at the highest contraction velocity (180°/s). Dynamic muscle quality was associated with reduced walking endurance (R=.689, P=.006 and R=.550, P=.042 for initial and absolute claudication distance, respectively). The claudicating-limb group demonstrated a trend towards reduced static muscle quality compared to controls (22%, P=.084). The relative contribution of the soleus muscle to plantarflexion maximum voluntary contraction was significantly higher in both claudicating-limb and asymptomatic-limb groups compared to controls (P=.012 and P=.018). Conclusions: The muscle strength of the plantarflexors in those with PAD-IC appears to be impaired at high contraction velocities. This may be explained by some reduction in gastrocnemii muscle quality and a greater reliance on the prominently type I fibred soleus muscle. The reduced dynamic capability of the plantarflexor muscles was associated with disease severity and walking ability, therefore efforts to improve plantarflexor power through dynamic exercise intervention are vital to maintain functional performance

Biomechanical demands of the 2-step transitional gait cycles linking level gait and stair descent gait in older women

Stair descent is an inherently complex form of locomotion posing a high falls risk for older adults, specifically when negotiating the transitional gait cycles linking level gait and descent. The aim of this study was to enhance our understanding of the biomechanical demands by comparing the demands of these transitions. Lower limb kinematics and kinetics of the 2-step transitions linking level and descent gait at the top (level-to-descent) and the bottom (descent-to-level) of the staircase were quantified in 36 older women with no falls history. Despite undergoing the same vertical displacement (2-steps), the following significant (p<.05) differences were observed during the top transition compared to the bottom transition: reduced step velocity; reduced hip extension and increased ankle dorsiflexion (late stance/pre-swing); reduced ground reaction forces, larger knee extensor moments and powers (absorption; late stance); reduced ankle plantarflexor moments (early and late stance) and increased ankle powers (mid-stance). Top transition biomechanics were similar to those reported previously for continuous descent. Kinetic differences at the knee and ankle signify the contrasting and prominent functions of controlled lowering during the top transition and forward continuance during the bottom transition. The varying musculoskeletal demands encountered during each functional sub-task should be addressed in falls prevention programmes with elderly populations where the greatest clinical impact may be achieved. Knee extensor eccentric power through flexion exercises would facilitate a smooth transition at the top and improving ankle plantarflexion strength during single and double limb stance activities would ease the transition into level gait following continuous descent

A meta-synthesis of qualitative studies of the link between anxiety, depression and perfectionism: Implications for treatment

Background: Meta-analyses show an association between perfectionism and depression and anxiety (negative affect), and that therapy for perfectionism impacts positively on negative affect. No systematic reviews have focused on qualitative studies of perfectionism. Aims: Our aim was to perform a systematic, meta-synthesis of qualitative literature to (i) help inform our understanding of how perfectionism is associated with negative affect, so that we can (ii) inform future development of treatment for perfectionism in young people and to make it more effective. Method: Included in the meta-synthesis were 37 qualitative studies. Results: Six themes related to perfectionism were found: (1) the association with negative affect, (2) self-worth dependent on achievement, (3) cognitive and behavioural maintaining factors, (4) the expectations of others, (5) effective elements of interventions, and (6) barriers to treatment. Conclusions: The qualitative literature supports the notion of perfectionism as an important construct to consider in reducing negative affect. While cognitive behavioural therapy for perfectionism holds promise as a treatment to target negative affect, there was a paucity of qualitative research, particularly related to young people. A greater understanding of the views of young people are required to help tailor more effective interventions for perfectionism that can impact negative affect in this group

Torque-onset determination: Unintended consequences of the threshold method.

BACKGROUND: Compared with visual torque-onset-detection (TOD), threshold-based TOD produces onset bias, which increases with lower torques or rates of torque development (RTD). PURPOSE: To compare the effects of differential TOD-bias on common contractile parameters in two torque-disparate groups. METHODS: Fifteen boys and 12 men performed maximal, explosive, isometric knee-extensions. Torque and EMG were recorded for each contraction. Best contractions were selected by peak torque (MVC) and peak RTD. Visual-TOD-based torque-time traces, electromechanical delays (EMD), and times to peak RTD (tRTD) were compared with corresponding data derived from fixed 4-Nm- and relative 5%MVC-thresholds. RESULTS: The 5%MVC TOD-biases were similar for boys and men, but the corresponding 4-Nm-based biases were markedly different (40.3±14.1 vs. 18.4±7.1ms, respectively; p<0.001). Boys-men EMD differences were most affected, increasing from 5.0ms (visual) to 26.9ms (4Nm; p<0.01). Men's visually-based torque kinetics tended to be faster than the boys' (NS), but the 4-Nm-based kinetics erroneously depicted the boys as being much faster to any given %MVC (p<0.001). CONCLUSIONS: When comparing contractile properties of dissimilar groups, e.g., children vs. adults, threshold-based TOD methods can misrepresent reality and lead to erroneous conclusions. Relative-thresholds (e.g., 5% MVC) still introduce error, but group-comparisons are not confounded

A realist synthesis of websites containing content on perfectionism: Are the descriptions and advice empirically supported?

BACKGROUND: Perfectionism is a risk factor for depression and anxiety and is increasing in young people. It is important to understand the information that youth are exposed to about perfectionism on the internet and what may be required to make this more helpful in terms of accessing empirically supported descriptions and advice. METHODS: This research used novel methodology to investigate content about perfectionism on websites by conducting a realist synthesis of the definitions of perfectionism, and the degree to which websites contain empirically supported strategies and recognise the advantages and disadvantages of perfectionism. The results were presented to people aged 18 to 24 (N = 18) with a lived experience of anxiety/depression for feedback. RESULTS: The search yielded 992 websites, 266 of which were included in the synthesis; only one met the criteria for excellent quality with most (56%) judged as moderate. The feelings, thoughts, and behaviours that accompany perfectionism were commonly described, and strategies included identifying cognitions and developing alternatives, moving from self-criticism to self-compassion, normalising mistakes, adjusting goals, receiving practical support, and strategies for procrastination. The young people wanted further emphasis on depression and anxiety as consequences of perfectionism that contributed to a vicious cycle. They identified interventions were difficult, with greater levels of support needed. CONCLUSIONS: While most websites contained empirically supported information, the quality needs to improve, and further information needs to be provided on the links with anxiety and depression. Interventions for perfectionism need to have more focus on helping young people develop support networks

Association between somatosensory, visual and vestibular contributions to postural control, reactive balance capacity and healthy ageing in older women.

We investigated the biological systems involved in maintaining equilibrium during unstable and perturbed conditions in 39 healthy older women and estimated the annual difference in performance across the older age spectrum using regression. The largest annual difference in equilibrium occurred when the somatosensory system received inaccurate feedback and visual input was removed. With age, weight distribution became asymmetric at the onset of backwards perturbations, possibly in preparation for executing a stepping strategy. When one sensory system was challenged, postural responses were stable suggesting other systems compensated. When multiple sensory systems were challenged, significant differences in postural control emerged with age