Aging and skeletal muscle force control: Current perspectives and future directions.

During voluntary muscle contractions, force output is characterized by constant inherent fluctuations, which can be quantified either according to their magnitude or temporal structure, that is, complexity. The presence of such fluctuations when targeting a set force indicates that control of force is not perfectly accurate, which can have significant implications for task performance. Compared to young adults, older adults demonstrate a greater magnitude and lower complexity in force fluctuations, indicative of decreased steadiness, and adaptability of force output, respectively. The nature of this loss-of-force control depends not only on the age of the individual but also on the muscle group performing the task, the intensity and type of contraction and whether the task is performed with additional cognitive load. Importantly, this age-associated loss-of-force control is correlated with decreased performance in a range of activities of daily living and is speculated to be of greater importance for functional capacity than age-associated decreases in maximal strength. Fortunately, there is evidence that acute physical activity interventions can reverse the loss-of-force control in older individuals, though whether this translates to improved functional performance and whether lifelong physical activity can protect against the changes have yet to be established. A number of mechanisms, related to both motor unit properties and the behavior of motor unit populations, have been proposed for the age-associated changes in force fluctuations. It is likely, though, that age-associated changes in force control are related to increased common fluctuations in the discharge times of motor units.

Physical Characteristics of Youth Elite Golfers and Their Relationship With Driver Clubhead Speed.

Coughlan, D, Taylor, M, Jackson, J, Ward, N, and Beardsley, C. Physical characteristics of youth elite golfers and their relationship with driver clubhead speed. J Strength Cond Res 34(1): 212-217, 2020-Increased clubhead speed (CHS) has a strong relationship with golf performance and is related to athletic qualities in adult golfers. Research investigating the youth golfer is limited. The purpose of this study was to explore the relationships between strength and power on CHS in youth golfers. A correlational design was used to assess relationships between CHS and anthropometric, strength, and power measurements. Thirty-six male and 33 female golfers aged 13-17 took part in this study. Male golfers showed significant relationships between CHS and handicap (HCP) (r = -0.50), seated medicine ball throw to the left (SMBTL) (r = 0.67), and right (SMBTR) (r = 0.61), rotational medicine ball throw to the left (RMBTL) (r = 0.71), and right RMBTR (r = 0.62). Female golfers showed significant relationships between CHS and HCP (r = -0.52), mass (r = 0.72), countermovement jump power (r = 0.60), RMBTL (r = 0.57), RMBTR (r = 0.56). Multiple stepwise linear regression analysis identified 77% of the variance in CHS could be explained through SMBTL and RMBTL in males. In females, 84% of the variance in CHS could be explained through mass, RMBTR, and height. This study demonstrated relationships between CHS and body mass and upper-, lower-, and full-body concentric dominant power exercises. This study could aid in the development of training interventions for youth golfers.

Biomechanics of wheelchair turning manoeuvres: novel insights into wheelchair propulsion.

Introduction: Wheelchair turning biomechanics is an under researched area despite its obvious relevance to functional mobility of wheelchair users. Wheelchair turns might be linked to a higher risk of upper limb injuries due to the increased forces and torques potentially associated with asymmetric movement. Our aim was to obtain a better theoretical understanding of wheelchair turning by biomechanically analyzing turns compared to steady-state straightforward propulsion (SSSFP). Methods: Ten able-bodied men received 12-min familiarization and 10 trials (in a random order) of SSSFP and multiple left and right turns around a rectangular course. A Smartwheel was mounted at the right wheel of a standard wheelchair to measure kinetic parameters during SSSFP and of the inner hand during right turns and the outer hand during left turns. A repeated measures ANOVA was used to detect differences across tasks. Results: Two strategies were identified: 3% demonstrated roll turns and 97% spin turns. Spin turns consisted of three phases: approach, turning and depart phase. The turning phase was accomplished by increasing peak force (72.9 ± 25.1 N vs. 43.38 ± 15.9 N in SSSFP) of the inner hand, while maintaining high push frequency of the outer hand (1.09 ± 0.20 push/s vs. 0.95 ± 0.13 push/s in SSSFP). Peak negative force and force impulse during the turning phase were much higher than SSSFP, 15.3 ± 15.7 and 4.5 ± 1.7 times higher, respectively. Conclusion: The spin turn strategy might carry an increased risk of upper limb injuries due to higher braking force and requires particular attention by rehabilitation professionals to preserve upper limb function of long-term wheelchair users.

Vertical jumping and leg power normative data for English school children aged 10-15 years.

Although vertical jumping is often incorporated into physical activity tests for both adults and children, normative data for children and adolescents are lacking in the literature. The objectives of this study were to provide normative data of jump height and predicted peak leg power for males and females aged 10.0-15.9 years. Altogether, 1845 children from 12 state primary and secondary schools in the East of England participated in the study. Each child performed two countermovement jumps, and jump height was calculated using a NewTest jump mat. The highest jump was used for analysis and in the calculation of predicted peak power. Jump height and predicted peak leg power were significantly higher for males than females from the age of 11 years. Jump height and peak power increased significantly year on year for males. For females, jump height and predicted peak leg power reached a plateau after age 12 and 13 years respectively. This study provides normative data that can be used as a tool to classify jumping performance in children aged 10-15 years.

The concept of margins of stability can be used to better understand a change in obstacle crossing strategy with an increase in age.

The purpose of the current study was to use the margins of stability (MoS) to investigate how older adults choose between minimizing the risk of a forward fall when crossing an obstacle and the ease of maintaining forward progression during the steps taken behind the obstacle. In the current study 143 community-dwelling older adults aged between 55 and 83 years old, were divided into three age groups based on tertials of age. All participants were asked to complete five trials of obstacle walking and five trials of normal walking. For the trials of normal walking, the main difference between groups was that MoS at initial contact was lower in the older age groups. For the trials of obstacle crossing the MoS at the instants of obstacle crossing with both the leading and trailing limb became smaller with an increase in age. This result might imply that older people choose to use a strategy during obstacle crossing that results in smaller chance of falling forward if an obstacle was struck. A negative consequence of this more conservative strategy was a smaller MoS at the instants of initial contact after crossing the obstacle, thus a larger chance of a backward fall. These findings provide more insight into the regulation of stability during obstacle crossing and specifically in the differences in strategy between younger and older people, and therefore these results might be used for further research to investigate whether obstacle crossing strategies are trainable in older adults, which could be used as advisory programs aimed at fall prevention and/or engagement in an active lifestyle.

Sex differences in wheelchair propulsion biomechanics and mechanical efficiency in novice young able-bodied adults.

An awareness of sex differences in gait can be beneficial for detecting the early stages of gait abnormalities that may lead to pathology. The same may be true for wheelchair propulsion. The aim of this study was to determine the effect of sex on wheelchair biomechanics and mechanical efficiency in novice young able-bodied wheelchair propulsion. Thirty men and 30 women received 12  min of familiarisation training. Subsequently, they performed two 10-m propulsion tests to evaluate comfortable speed (CS). Additionally, they performed a 4-min submaximal propulsion test on a treadmill at CS, 125% and 145% of CS. Propulsion kinetics (via Smartwheel) and oxygen uptake were continuously measured in all tests and were used to determine gross mechanical efficiency (GE), net efficiency (NE) and fraction of effective force (FEF). Ratings of perceived exertion (RPE) were assessed directly after each trial. Results indicated that CS for men was faster (0.98 ± 0.24 m/s) compared to women (0.71 ± 0.18 m/s). A lower GE was found in women compared to men. Push percentage, push angle and local RPE were different across the three speeds and between men and women. NE and FEF were not different between groups. Thus, even though their CS was lower, women demonstrated a higher locally perceived exertion than men. The results suggest sex differences in propulsion characteristics and GE. These insights may aid in optimising wheelchair propulsion through proper training and advice to prevent injuries and improve performance. This is relevant in stimulating an active lifestyle for those with a disability.

Are there associations with age and sex in walking stability in healthy older adults?

The variability of the centre of pressure (COP) during walking can provide information in relation to stability when walking. The aim of this study was to investigate if age and sex were associated with COP variability, COP excursions, and COP velocities during walking. One-hundred and fourteen older adults (age 65.1±5.5 yrs.) participated in the study. A Kistler force platform (1000Hz) recorded the ground reaction forces and COPs during walking at a self-selected walking speed. The stance phase was divided, using the vertical GRF, into four sub-phases: loading response (LR), mid-stance (MSt), terminal stance (TSt), and pre-swing (PSw). The standard deviations of the COP displacement (variability), the COP velocity, and COP excursion in the medial-lateral and anterior-posterior directions, as well as the resultant magnitude were assessed. When controlling for walking speed, a greater age was associated with a higher variability and excursion of the COP during LR only suggesting that stability is maintained during the majority of the stance phase. During LR lower COP velocity was significantly associated for females for anterior-posterior and total COP, which may be a strategy to facilitate stability before, and moving into, MSt and TSt.

Biomechanics in Paralympics: Implications for Performance.

PURPOSE: To provide an overview of biomechanical studies in Paralympic research and their relevance for performance in Paralympic sports. METHODS: The search terms paralympic biomechanics, paralympic sport performance, paralympic athlete performance, and paralympic athlete were entered into the electronic database PubMed. RESULTS: Thirty-four studies were found. Biomechanical studies in Paralympics mainly contributed to performance enhancement by technical optimization (n = 32) and/or injury prevention (n = 6). In addition, biomechanics was found to be important in understanding activity limitation caused by various impairments, which is relevant for evidence-based classification in Paralympic sports (n = 6). Distinctions were made between biomechanical studies in sitting (41%), standing (38%), and swimming athletes (21%). In sitting athletes, mostly kinematics and kinetics in wheelchair propulsion were studied, mainly in athletes with spinal-cord injuries. In addition, kinetics and/or kinematics in wheelchair basketball, seated discus throwing, stationary shot-putting, hand-cycling, sit-skiing, and ice sledge hockey received attention. In standing sports, primarily kinematics of athletes with amputations performing jump sports and running and the optimization of prosthetic devices were investigated. No studies were reported on other standing sports. In swimming, mainly kick rate and resistance training were studied. CONCLUSIONS: Biomechanical research is important for performance by gaining insight into technical optimization, injury prevention, and evidence-based classification in Paralympic sports. In future studies it is advised to also include physiological and biomechanical measures, allowing the assessment of the capability of the human body, as well as the resulting movement.

The impact of mobile phone use on where we look and how we walk when negotiating floor based obstacles.

Pedestrians regularly engage with their mobile phone whilst walking. The current study investigated how mobile phone use affects where people look (visual search behaviour) and how they negotiate a floor based hazard placed along the walking path. Whilst wearing a mobile eye tracker and motion analysis sensors, participants walked up to and negotiated a surface height change whilst writing a text, reading a text, talking on the phone, or without a phone. Differences in gait and visual search behaviour were found when using a mobile phone compared to when not using a phone. Using a phone resulted in looking less frequently and for less time at the surface height change, which led to adaptations in gait by negotiating it in a manner consistent with adopting an increasingly cautious stepping strategy. When using a mobile phone, writing a text whilst walking resulted in the greatest adaptions in gait and visual search behaviour compared to reading a text and talking on a mobile phone. Findings indicate that mobile phone users were able to adapt their visual search behaviour and gait to incorporate mobile phone use in a safe manner when negotiating floor based obstacles.

Fixation failure in an isolated tibial eminence ACL traction avulsion fracture in a paratrooper: is there an association with vitamin D deficiency?

Tibial eminence avulsion fracture at the ACL footprint may be caused by high-energy forces such as a fall, in which the ACL ligament proves stronger than the forces that hold the bone together. For reasons of bone maturity however, tibial spine avulsion fractures where the ACL remains intact, typically occur in children but are rare in adults. This case demonstrates a rare type of adult tibial avulsion fracture with intact ACL and subsequent fragment fixation failure in which vitamin D deficiency may have been contributory. Because there is a high rate of inadequate vitamin D levels in patients undergoing orthopaedic surgery and a known impact on bone healing complications, post-operative bone fixation failure may also occur. This case report may therefore prompt further awareness for considering pre-surgical vitamin D deficiency screening in adults presenting with rare avulsion fractures, and may further demonstrate its impact on surgical outcomes.

Comparing the Energy Expenditure of Wii Fit(™)-Based Therapy Versus Traditional Physiotherapy.

OBJECTIVE: Activity-promoting computer gaming systems, which encourage the use of the body to control game play, are commonly used in rehabilitation. However, the mechanisms by which improvements in clinical outcomes occur after using activity-promoting gaming systems are unknown. Therefore the aims of this study were to compare the physiological cost and enjoyment of Nintendo(®) (Kyoto, Japan) Wii Fit™-based therapy compared with traditional-based physiotherapy training. SUBJECTS AND METHODS: Young adults (n=35), 20.7±1.6 years old, carried out a traditional physiotherapy training program and a Wii Fit-based training program. Energy expenditure was assessed using indirect calorimetry while at rest and during training modes, and enjoyment was measured using a modified Physical Activity Enjoyment Scale. RESULTS: For the traditional physiotherapy-based program, all physiological measures (oxygen consumption [VO2], energy expenditure, and metabolic equivalents [METs]) were significantly greater (VO2, 0.64 versus 0.51 L/minute; energy expenditure, 186.0 versus 146.5 J/kg/minute; METs, 2.6 versus 2.1) than for the Wii Fit-based program. Enjoyment was rated statistically significantly higher for the Wii Fit-based program (76.0±13.7 percent) compared with the traditional program (67.5±14.8 percent). CONCLUSIONS: The lower physiological cost associated with the Wii Fit suggests that it is less demanding than the traditional therapy, even though this modality of training has been shown to elicit improvements in rehabilitative outcomes. This suggests that frailer individuals, whose energy levels are impaired, may benefit from using the Wii Fit as a rehabilitative tool because of the lower demand on energy.

Activity-promoting gaming systems in exercise and rehabilitation.

Commercial activity-promoting gaming systems provide a potentially attractive means to facilitate exercise and rehabilitation. The Nintendo Wii, Sony EyeToy, Dance Dance Revolution, and Xbox Kinect are examples of gaming systems that use the movement of the player to control gameplay. Activity-promoting gaming systems can be used as a tool to increase activity levels in otherwise sedentary gamers and also be an effective tool to aid rehabilitation in clinical settings. Therefore, the aim of this current work is to review the growing area of activity-promoting gaming in the context of exercise, injury, and rehabilitation.

What gives Bolt the edge-A.V. Hill knew it already!

The 100 m is the blue ribboned event of world athletics competitions, with the winner crowned as the fastest human on Earth. Currently that fastest human is Usain Bolt, who covers 100 m in 9.58 s, achieving an average velocity of 10.43 m s(-1). Bolt is a phenomenal athlete, but what is his trick? Using Hills model, relating muscle force and heat liberation to shortening velocity, we propose that Bolt is at an advantage in relative power development and biomechanical efficiency compared to his contemporaries.

The temporal-spatial and ground reaction impulses of turning gait: is turning symmetrical?

This study had two aims. Firstly, to characterise the temporal-spatial and ground reaction impulse adjustments, compared to straight gait, required to complete step turns to the left and to the right and secondly, to assess if the turns were asymmetrical. Seven participants were instructed to perform 90 degrees step turns to the left and right. The actual angle turned was less for both turns (right 80.2+/-5.5 degrees , left 82.8+/-5.3 degrees ). Data were collected using a 7 camera VICON infra-red motion analysis system (120 Hz) and a Kistler force plate (600 Hz). Adjustments were made in the approach, turn and depart strides compared to straight gait. The mean velocity was significantly lower and the stride was significantly shorter in the approach stride before the turn (p<0.0125) compared to straight gait, indicating a possible feed-forward mechanism prior to turning. Velocity was significantly lower and the stride length significantly shorter during the depart stride (p<0.0125) compared to straight gait. Participants did not return to a normal pattern within one stride. For the turn step, the velocity, step length and step width were all significantly different (p<0.0125) compared to straight gait. The turning ground reaction impulses were significantly greater (p<0.0125) compared to straight gait, indicating a need for increased support, medial shift, braking and propulsion. The turns to the left and right were statistically asymmetrical (p<0.0125) in 11 of the 18 variables. However, impulses were generally symmetrical, which does not generally support the functional asymmetry theory, though the contributions to propulsion were significantly greater when turning from the dominant limb.