In vivo oscillations of the soleus muscle can be quantified using b-mode ultrasound imaging during walking and running in humans

Impact forces, due to the foot contacting the ground during locomotion, can be considered input signals to the body that must be dissipated to prevent impact-related injuries. One proposed mechanism employed by the body to damp the impact is through vibrations of the skeletal muscles. However, there is yet to be direct in vivo measures of muscle oscillations during locomotion. This study investigated the use of 2D ultrasound imaging to quantify transverse muscle oscillations (deep-superficial displacement of the muscle boundary relative to the skin) in response to impact forces elicited by walking and running at a range of speeds. Increases in vertical impact forces with faster walking and running was consistent with changes in both magnitude and frequency in the measured oscillations of the soleus muscle; one of the main human ankle plantar flexors. Muscle oscillations contained more higher frequency components at fast running (50% signal power in frequencies below ~ 14 Hz) compared with slow walking (50% signal power contained in frequencies below ~ 5 Hz). This study provides a platform for ultrasound imaging to examine muscle oscillation responses to impact forces induced by changes in external interfaces such as shoe material, locomotion type and ground surface properties

Children with developmental coordination disorder have less variable motor unit firing rate characteristics across contractions compared to typically developing children

Introduction: Understanding the nuances of neuromuscular control is crucial in unravelling the complexities of developmental coordination disorder (DCD), which has been associated with differences in skeletal muscle activity, implying that children with DCD employ distinct strategies for muscle control. However, force generation and control are dependent on both recruitment of motor units and their firing rates and these fine details of motor function have yet to be studied in DCD. The purpose of this study was therefore to compare motor unit characteristics in a small muscle of the hand during low level, handgrip contractions in typically developing (TD) children and children with DCD. Methods: Eighteen children (9 TD vs. 9 DCD) completed a series of manual handgrip contractions at 10 ± 5% of their maximum voluntary contraction. High density surface electromyography was used to record excitation of the first dorsal interosseus muscle. Recorded signals were subsequently decomposed into individual motor unit action potential trains. Motor unit characteristics (firing rate, inter-pulse interval, and action potential amplitude) were analysed for contractions that had a coefficient variation of <10%. Results and Discussion: This study found few differences in average motor unit characteristics (number of motor units: TD 20.24 ± 9.73, DCD 27.32 ± 14.00; firing rate: TD 7.74 ± 2.16 p.p.s., DCD 7.86 ± 2.39 p.p.s.; inter-pulse interval: TD 199.72 ± 84.24 ms, DCD 207.12 ± 103 ms) when force steadiness was controlled for, despite the DCD group being significantly older (10.89 ± 0.78 years) than the TD group (9.44 ± 1.67 years). However, differences were found in the variability of motor unit firing statistics, with the children with DCD surprisingly showing less variability across contractions (standard deviation of coefficient of variation of inter-pulse interval: TD 0.38 ± 0.12, DCD 0.28 ± 0.11). This may suggest a more fixed strategy to stabilise force between contractions used by children with DCD. However, as variability of motor unit firing has not been considered in previous studies of children further work is required to better understand the role of variability in motor unit firing during manual grasping tasks, in all children

An In-shoe Temperature Measurement System for Studying Diabetic Foot Ulceration Etiology: Preliminary Results with Healthy Participants

AbstractDiabetes is a major public health challenge on a global scale but our scientific understanding of diabetic foot ulceration is limited. A recent systematic review concluded that an increase in skin temperature is predictive of foot ulceration. In-shoe temperature measurement could be a useful tool for studying the etiology of diabetic foot ulceration, we present such a device and preliminary results of its use with 14 healthy participants. Our results show that temperature rise with walking mainly depends on the speed, F(2,190)=3.75, p=0.025, the effect of foot location is mild F(3,1279)=1.69, p=0.169, and there is no difference between the two feet F(1,1279)=0.937, p=0.749. We conclude that such systems are feasible but there are measurement issues to be addressed before they can be utilized further

Maturity associated differences in match running performance in elite male youth soccer players

Purpose: To investigate the influence of maturation on match running performance in elite male youth soccer players. Methods: A total of 37 elite male youth soccer participants from an English professional soccer academy from the U14s, U15s, and U16s age groups were assessed over the course of 1 competitive playing season (2018-2019). Relative biological maturity was assessed using percentage of predicted adult height. A global positioning system device was used between 2 and 30 (mean = 8 [5]) times on each outfield player. The position of each player in each game was defined as defender, midfielder, or attacker and spine or lateral. A total of 5 match-running metrics were collected total distance covered, high-speed running distance, very high-speed running distance, maximum speed attained, and number of accelerations. Results: Relative biological maturity was positively associated with all global positioning system running metrics for U14s. The U15/16s showed variation in the associations among the global positioning system running metrics against maturity status. A multilevel model which allowed slopes to vary was the best model for all parameters for both age groups. In the U14 age group, advanced maturation was associated with greater high-speed running distance. However, maturation did not contribute toward variance in any of the indices of running performance in the U15/16s. In the U15/16 age group, significance was observed in the spine/lateral playing positions when undertaking actions that required covering distance at high speeds. Conclusions: Maturation appeared to have an impact on match-running metrics within the U14s cohort. However, within the U15/16s, the influence of maturation on match-running metrics appeared to have less of an impact

Physical and electrophysiological motor unit characteristics are revealed with simultaneous high-density electromyography and ultrafast ultrasound imaging

Electromyography and ultrasonography provide complementary information about electrophysiological and physical (i.e. anatomical and mechanical) muscle properties. In this study, we propose a method to assess the electrical and physical properties of single motor units (MUs) by combining High-Density surface Electromyography (HDsEMG) and ultrafast ultrasonography (US). Individual MU firings extracted from HDsEMG were used to identify the corresponding region of muscle tissue displacement in US videos. The time evolution of the tissue velocity in the identified region was regarded as the MU tissue displacement velocity. The method was tested in simulated conditions and applied to experimental signals to study the local association between the amplitude distribution of single MU action potentials and the identified displacement area. We were able to identify the location of simulated MUs in the muscle cross-section within a 2 mm error and to reconstruct the simulated MU displacement velocity (cc > 0.85). Multiple regression analysis of 180 experimental MUs detected during isometric contractions of the biceps brachii revealed a significant association between the identified location of MU displacement areas and the centroid of the EMG amplitude distribution. The proposed approach has the potential to enable non-invasive assessment of the electrical, anatomical, and mechanical properties of single MUs in voluntary contractions

Children with developmental coordination disorder are less able to fine-tune muscle activity in anticipation of postural perturbations than typically developing counterparts

The majority of children with developmental coordination disorder (DCD) struggle with static and dynamic balance, yet there is limited understanding of the underlying neuromechanical mechanisms that underpin poor balance control in these children. Eighteen children with DCD and seven typically developing (TD) children aged 7–10 years stood with eyes open on a moveable platform progressively translated antero-posteriorly through three frequencies (0.1, 0.25 and 0.5 Hz). Myoelectric activity of eight leg muscles, whole-body 3D kinematics and centre of pressure were recorded. At each frequency, postural data were divided into transition-state and steady-state cycles. Data were analyzed using a linear mixed model with follow-up Tukey’s pairwise comparisons. At the slowest frequency, children with DCD behaved like age-matched TD controls. At the fastest frequency, children with DCD took a greater number of steps, had a greater centre of mass variability, had a greater centre of pressure area, and tended to activate their muscles earlier and for longer than TD children. Children with DCD did not alter their postural response following prolonged exposure to platform movement, however they made more, non-structured postural adjustments in the medio-lateral direction as task difficulty increased. At the faster oscillation frequencies, children with DCD adopted a different muscle recruitment strategy to TD children. Activating their muscles earlier and for longer may suggest that children with DCD attempt to predict and react to postural disturbances, however the resulting anticipatory muscle excitation patterns do not seem as finely tuned to the perturbation as those demonstrated by TD children. Future work should examine the impact of balance training interventions on the muscle recruitment strategies of children with DCD, to ensure optimal interventions can be prescribed

The mobility limitation in healthy older people is due to weakness and not slower muscle contractile properties.

The maximal power generating capacity of a muscle declines with age and has a negative impact on the performance of daily life activities. As muscle power is the product of force and velocity, we recruited 20 young (10 men, 10 women: 20-31 years) and 20 older (10 men, 10 women: 65-86 years) people to investigate which of these components contributes to the lower power and performance in old age. After determination of the maximal isometric knee extension torque (MVC), they performed a countermovement jump (CMJ) in 1) the normal situation (normal), 2) with an extra load of 15% body weight (loaded) and 3) 15% lower body weight (unloaded with a pulley system), and a timed up-and-go test (TUG) in the normal or loaded condition. The TUG and CMJ performance was lower in old than young participants (p<0.001). Below a critical CMJ peak power of ~23.7 W·kg-1 TUG showed a progressive decrease. The CMJ take-off velocity (Voff) in the normal condition was lower in old than young participants (p<0.001). However, the Voff vs. body weight/MVC relationship of the normal, loaded and unloaded data combined was similar in the old and young participants and fitted the Hill equation (R2 = 0.396). This indicates that 1) only when peak power drops below a critical threshold TUG becomes impaired and 2) there was no evidence for intrinsic slowing of the muscle contractile properties in older people, but rather the older people were working on a slower part of the force-velocity relationship due to weaker muscles

Estimating skeletal muscle fascicle curvature from B-mode ultrasound image sequences

We address the problem of tracking in vivo muscle fascicle shape and length changes using ultrasound video sequences. Quantifying fascicle behavior is required to improve understanding of the functional significance of a muscle's geometric properties. Ultrasound imaging provides a noninvasive means of capturing information on fascicle behavior during dynamic movements; to date however, computational approaches to assess such images are limited. Our approach to the problem is novel because we permit fascicles to take up nonlinear shape configurations. We achieve this using a Bayesian tracking framework that is: 1) robust, conditioning shape estimates on the entire history of image observations; and 2) flexible, enforcing only a very weak Gaussian Process shape prior that requires fascicles to be locally smooth. The method allows us to track and quantify fascicle behavior in vivo during a range of movements, providing insight into dynamic changes in muscle geometric properties which may be linked to patterns of activation and intramuscular forces and pressures

Regular endurance exercise of overloaded muscle of young and old male mice does not attenuate hypertrophy and improves fatigue resistance

It has been observed that there is an inverse relationship between fiber size and oxidative capacity due to oxygen, ADP, and ATP diffusion limitations. We aimed to see if regular endurance exercise alongside a hypertrophic stimulus would lead to compromised adaptations to both, particularly in older animals. Here we investigated the effects of combining overload with regular endurance exercise in young (12 months) and old (26 months) male mice. The plantaris muscles of these mice were overloaded through denervation of synergists to induce hypertrophy and the mice ran on a treadmill for 30 min per day for 6 weeks. The hypertrophic response to overload was not blunted by endurance exercise, and the increase in fatigue resistance with endurance exercise was not reduced by overload. Old mice demonstrated less hypertrophy than young mice, which was associated with impaired angiogenesis and a reduction in specific tension. The data of this study suggest that combining endurance exercise and overload induces the benefits of both types of exercise without compromising adaptations to either. Additionally, the attenuated hypertrophic response to overload in old animals may be due to a diminished capacity for capillary growth

Endurance exercise plus overload induces fatigue resistance and similar hypertrophy in mice irrespective of muscle mass.

NEW FINDINGS:What is the central question of this study? Does combining endurance and hypertrophic stimuli blunt the adaptations to both modalities and is this effect greater in muscles with larger baseline fibre cross sectional area? What is the main finding and its importance? Endurance exercise and hypertrophic stimuli can be combined to increase fatigue resistance and fibre size without blunting either adaptation regardless of baseline fibre size. ABSTRACT:Previous studies have demonstrated that fibre cross-sectional area (FCSA) is inversely related to oxidative capacity, which is thought to be determined by diffusion limitations of oxygen, ADP and ATP. Consequently, it is hypothesised that (1) when endurance training is combined with a hypertrophic stimulus the response to each will be blunted, and (2) muscles with a smaller FCSA will show a larger hypertrophic response than those with a large FCSA. To investigate this, we combined overload with endurance exercise in 12-month-old male mice from three different strains with different FCSA: Berlin High (BEH) (large fibres), C57BL/6J (C57) (normal-sized fibres) and Berlin Low (BEL) (small fibres). The right plantaris muscle was subjected to overload through denervation of synergists with the left muscle acting as an internal control. Half the animals trained 30 min per day for 6 weeks. The overload-induced hypertrophy was not blunted by endurance exercise, and the exercise-induced increase in fatigue resistance was not impaired by overload. All strains demonstrated similar absolute increases in FCSA, although the BEH mice with more fibres than the C57 mice demonstrated the largest increase in muscle mass and BEL mice with fewer fibres the smallest increase in muscle mass. This study suggests that endurance exercise and hypertrophic stimuli can be combined without attenuating adaptations to either modality, and that increases in FCSA are independent of baseline fibre size