Can segmental model reductions quantify whole-body balance accurately during dynamic activities?

When investigating whole-body balance in dynamic tasks, adequately tracking the whole-body centre of mass (CoM) or derivatives such as the extrapolated centre of mass (XCoM) can be crucial but add considerable measurement efforts. The aim of this study was to investigate whether reduced kinematic models can still provide adequate CoM and XCoM representations during dynamic sporting tasks. Seventeen healthy recreationally active subjects (14 males and 3 females; age, 24.9±3.2years; height, 177.3±6.9cm; body mass 72.6±7.0kg) participated in this study. Participants completed three dynamic movements, jumping, kicking, and overarm throwing. Marker-based kinematic data were collected with 10 optoelectronic cameras at 250Hz (Oqus Qualisys, Gothenburg, Sweden). The differences between (X)CoM from a full-body model (gold standard) and (X)CoM representations based on six selected model reductions were evaluated using a Bland-Altman approach. A threshold difference was set at ±2cm to help the reader interpret which model can still provide an acceptable (X)CoM representation. Antero-posterior and medio-lateral displacement profiles of the CoM representation based on lower limbs, trunk and upper limbs showed strong agreement, slightly reduced for lower limbs and trunk only. Representations based on lower limbs only showed less strong agreement, particularly for XCoM in kicking. Overall, our results provide justification of the use of certain model reductions for specific needs, saving measurement effort whilst limiting the error of tracking (X)CoM trajectories in the context of whole-body balance investigation

THE ROLE OF TARGET LOCATION ON THE INTERACTION BETWEEN POSTURAL BALANCE MECHANISMS AND END-EFFECTOR PERFORMANCE IN THE TENNIS SERVE

The purpose of this study was to evaluate the relationship between end-effector (tennis racket) performance and postural balance across 4 serving locations. Eleven right-handed experienced tennis players participated in this study. Participants completed 10 successful tennis serves each to 4 serving locations. 12 optoelectronic cameras at 200 Hz (BTS bioengineering, Milan, Italy) were used to collect whole-body kinematic data. Statistical parametric mapping (SPM) with regression was used to identify the relationship between postural balance control (extrapolated centre of mass displacement and changes in arms/trunk angular momentum in forward/backward direction; 1D data) and end-effector performance (maximum racket forward velocity, 0D data) across the four serving locations. The results showed no systematic relationship between postural balance control mechanisms and end-effector performance across 4 different serving locations. It was concluded that serving to different locations likely involves different balance control mechanisms to adjust for target-specific serve technique constraints. For practical application, we found no evidence that balance control and end-effector performance are tightly related within elite tennis serve performance and that these could be trained separately

HOW DOES WHOLE BODY BALANCE CONTROL INTERACT WITH STROKE PERFORMANCE DURING THE TENNIS SERVE?

The purpose of this study was to investigate whether there is an interaction between mechanisms used to control whole body balance and racket performance. Fourteen experienced tennis players (nine males and five females; age, 21.5±3.9 yr; height, 1.7± 0.1 m; body mass 65.8± 8.1 kg) completed 10 successful tennis serves. Twelve optoelectronic cameras were used to collect kinematic data at 200 Hz (BTS bioengineering, Milan, Italy). Linear regression using 1D Statistical Parametric Mapping was used to identify interactions between the extrapolated centre of mass (XCoM) displacement in the anteroposterior direction and the changes in arms/trunk segment angular momentum, and peak anterior-posterior racket velocity. Overall, no meaningful relationships were found, except for a small time interval during the forward swing phase in which a greater increase in trunk angular momentum was associated with increased maximum racket velocity

Biomechanical aspects of postural balance strategy in dynamic sport activities

Postural balance is one of the most important aspects of everyday movement, especially in complex movements such as jumping, kicking or movements involving overhead/arm motion. In sporting activities, players often need to complete goal-directed tasks of an end-effector (e.g. tennis racket), while also needing to control their balance, in order to produce a successful task. However, studying the interaction between postural balance and end-effector control, in a biomechanical context and particularly in the tennis serve is difficult and remains largely unexplored. Traditionally, to explore postural balance researchers have to observe the whole-body centre of mass (CoM) location. However, for marker-based motion capture systems, collecting and processing data is time-consuming. If the researchers are interested in examining the movements of only some parts of the body, then reductions in model complexity may be possible while still retaining an ability to track CoM location. Therefore, the first aim of this research was to find an appropriate biomechanical model to quantify accurate whole-body (X)CoM representation. The second aim was then to investigate the interaction between postural balance control and end-effector performance, during the tennis serve, within a single target location and between different serving locations. The first study of this thesis showed that anteroposterior and medio-lateral displacement profiles of the CoM representation, based on the lower limbs, trunk and upper limbs showed strong agreement with the full-body model, and this only slightly reduced for the lower limbs and trunk only. Representations based on the lower limbs only showed less agreement, particularly for the extrapolated CoM (XCoM) in kicking. Our results justified the use of some model reductions for specific needs, saving measurement effort whilst limiting the error of tracking (X)CoM trajectories in the context of whole-body balance investigation. The second study of this thesis demonstrated that there is no direct interaction between the XCoM displacement, the changes in arms/trunk angular momentum, and maximum racket velocity during the preparation, propulsion and forward swing phases of a tennis serve. Only in the forward swing phase, a significant relationship between trunk angular momentum and maximum racket velocity was found which means the trunk segmental acceleration may play a role in controlling balance when generating the maximum racket velocity during the serve towards this target location. The third and final study in this thesis focussed on only the forward swing phase, and indicated that only the change in arms angular momentum influenced the maximum racket velocity. This was found specifically when serving into the wider part of the advantage court. Furthermore, individual relationships were evident between serving conditions. The novel approach introduced in this thesis, and the key outcomes of the work, have the potential to give researchers, coaches and athletes, who are working and playing in relevant dynamic sporting tasks, an opportunity to better understand the interaction between how control of the end-effector adapts while maintaining postural stability during the serve. Moreover, the work also guides the choice of biomechanical marker sets to estimate the centre of mass during dynamic activity

HOW DO TENNIS PLAYERS CONTROL THEIR BALANCE DURING THE SERVE?

The purpose of this study was to investigate how postural balance is manifested in high level tennis players, and whether movement variability is phase dependent. Twelve experienced tennis players (8 males and 4 females; age 21.5±4.11 years; height 174.75±6.06 cm; body mass 66.83±8.12 kg) completed 10 tennis successful serves. Whole-body kinematics were recorded and whole-body extrapolated centre of mass trajectories calculated. Within-subject variation was presented temporally to evaluate phase-dependent differences. Overall, our results showed individual balance control preferences and a progressive increase of within-subject variability throughout the serve movement. This knowledge will help trainers and coaches identify learning and performance needs associated to whole-body balance control

Development and study on physical and sensory properties of dark chocolates fortified with anthocyanin from broken riceberry rice

วารสารวิชาการและวิจัย มทร.พระนคร, ปีที่ 14, ฉบับที่ 2 (ก.ค.-ธ.ค. 2563), หน้า 45-56Broken rice of Thai cross breed black rice, Riceberry, was an under-utilized agricultural by-product that contains high content of anthocyanins, the multiple health benefits flavonoid. In this study, these anthocyanins were used to develop healthy dark hocolates. The anthocyanin extract from the broken Riceberry rice was prepared into anthocyanin powder using freeze-drying technique in which maltodextrin was used as a carrier material. Healthy dark chocolates were prepared by replacing cocoa powder with anthocyanin powder by 5, 10 and 15 g/g cocoa powder, which respectively delivers DC5, DC10, and DC15 anthocyanin-fortified dark chocolate bars. The color analysis showed no blooming (undesired white color at the chocolate surface) in all chocolates. The increase the anthocyanin powder content significantly decreased the hardness of the dark chocolates (33.9-27.2 N). Total anthocyanin content (TAC) in the dark chocolates increased respectively as anthocyanin powder content increased. The health benefit of the anthocyanin-fortified dark chocolates was improved as the DPPH antioxidant activity of all treatments was 4-9% higher than that of the control DC0. Sensory evaluation revealed that DC10 received higher liking scores (6.4-7.5) than the DC0 indicating more consumer preference. The anthocyanin-fortified dark chocolate delivers an alternative strategy to improve the health property of chocolates. This application of anthocyanin from the broken Riceberry rice could help increase the value and the utilization of Thai agricultural by-product.Rajamangala University of Technology Phra Nakho

Spatiotemporal and kinematic adjustments in master runners may be associated with the relative physiological effort during running

Master runners maintain a similar running economy to young runners, despite displaying biomechanical characteristics that are associated with a worse running economy. This apparent paradox may be explained by a greater physiological effort—i.e., percentage of maximal oxygen uptake (VO2-max)—that master runners perform at a given speed. Moreover, age-related responses to non-exhaustive sustained running are yet underexplored. The aims of this study were, therefore, to examine if biomechanical adjustments in master runners are physiological-effort dependent, and to explore the age-related biomechanical changes during a non-exhaustive sustained run. Young (23.9 ± 6; n = 12) and master (47.3 ± 6.9; n = 12) runners performed a sustained 30-minute treadmill run matched for relative physiological effort (70% VO2-max), while spatiotemporal and lower-limb kinematic characteristics were collected during the 1st and 30th minute. Group differences were observed in step/stride length, knee touch-down angle, and knee stiffness. However, both groups of runners had a similar step frequency, vertical center of mass oscillation, and knee range of motion. Age-related adjustment in these latter characteristics may thus not be an inevitable result of the aging process but rather a strategy to maintain running economy. The relative physiological effort of runners should, therefore, be considered when examining age-related adjustments in running biomechanics.</p