Qualisys Motion Capture System Research Articles

Effects of Task Constraints on Kinematic Characteristics of Body Segments in Children with Cerebral Palsy and Children with Typical Development during Hand-Reaching

Background: Children with cerebral palsy (CP) have difficulty in managing postural control during functional reaching tasks, although children with different postural control ability are able to come up with different motor solutions to cope with different task demands. This study examined the effect of task constraint on postural control performance in children with cerebral palsy and typical development (TD) in terms of different postural control abilities. Methods: A cross-sectional research design was used. Twelve children with spastic diplegic cerebral palsy (mean age: 107.8 months) and 16 typically developing children (mean age: 110.9 months) participated in this study. Individually, all subjects were seated in a height-adjusted chair and were requested to reach for target(s) located at three different directions (medial, anterior, and lateral). A six-camera Qualisys Motion Capture System was used to capture motion data. Kinematic data in terms of body alignment and angular changes were analyzed. Results: Children with cerebral palsy demonstrated different postural control strategies to complete different reaching tasks compared to typically developing children by preparing postural alignment in advance, coordinating different body orientation movements during reaching after showing difficulty in managing reach medially. Conclusions: Children with cerebral palsy perceive their insufficient ability and prepare their alignment in advance to adapt to the task demanded and decrease the postural challenges of the task. Even though children with cerebral palsy self-generate different motor solutions to reach without falling, these alternative strategies might not be the most efficient adaptation.

Task-Based Design Approach: Development of a Planar Cable-Driven Parallel Robot for Upper Limb Rehabilitation

This paper deals with the optimal design of a planar cable-driven parallel robot (CDPR), with three degrees of freedom, intended for assisting the patient’s affected upper limb along a prescribed movement. A Qualisys motion capture system was used to record the prescribed task performed by a healthy subject. For each pose taken by the center of mass of the end-effector, the cable tensions, the elastic stiffness and the dexterity were optimized while satisfying a set of constraints. First, a multiobjective formulation of the optimization problem was adopted. Since selecting a single solution among the multiple ones given by the Pareto front presents an issue, a mono-objective formulation was chosen, where the objective function was defined as a weighted sum of the chosen criteria. The appropriate values of the weighted coefficients were studied with the aim of identifying their influence on the optimization process and, thus, a judicious choice was made. A prototype of the optimal design of the CDPR was developed and validated experimentally on the prescribed workspace using the position control approach for the motors. The tests showed promising reliability of the proposed design for the task.

TN HYDROGELS AS A POTENTIAL ANTI-INFLAMMATORY DRUG DELIVERY SYSTEM TARGETED TO OSTEOARTHRITIC KNEES

Arthritis affects 26.3% of adults and approximately 50,000 children in the United States [1]. Hydrogel drug-delivery systems have been considered as a viable option for drug delivery to arthritic articular cartilage in the knee. To determine physiologically relevant loading, a Qualisys motion capture system was used to analyze the gait of college-aged females as they took several steps on a flat surface, then stepped onto a force plate. The motion capture and force plate data was used to determine maximum force exerted on the knee during normal gait. Three different alginate-based hydrogels, where the superior one had a triple interpenetrating graphene oxide network (TN hydrogels), were investigated for use as an antiinflammatory drug delivery system in a human knee joint. Physiologically relevant cyclic loading was performed to ensure that the TN hydrogel could withstand the force exerted in the knee. The TN hydrogel experienced a change in energy of 50% after cyclic loading (10.6 ± 15.0 Pa) and survived high stresses of 4 kPa, which is 80 magnitudes larger than observable gait forces as measured in this study. From a mechanical perspective, TN hydrogel appears to be mechanically viable for arthritis drug delivery. In addition, based on calculations and Flory-Rehner equations, the pore size of the TN hydrogel is adequate for encapsulating most NSAIDs, which have a molecule size ≤ 5μm.

Kinetics, kinematics, and knee muscle activation during sit to stand transition in unilateral and bilateral knee osteoarthritis

BackgroundThe sit to stand transition (STS) is a task performed by those with knee osteoarthritis (KOA) with biomechanical modifications that may influence the lower limb load distribution. As a weight bearing task mainly performed in the sagittal plane, the presence of unilateral or bilateral KOA may lead to asymmetry during its performance. Research questionAre the biomechanical and neuromuscular aspects of the sit to stand transition (STS) different between participants with unilateral and bilateral KOA? MethodsTwenty-eight participants were allocated as follows: unilateral KOA (OAUNI; n = 12) and bilateral KOA (OABI; n = 16). All participants were evaluated by means of kinematics (Qualisys Motion Capture System, Qualisys Medical AB, SUE), kinetics (Bertec Corporation's model 4060−08 Mod., USA), and electromyography (TrignoTM Wireless System, DelSys Inc., USA) during the STS. The variables calculated were the symmetry indices of the total support moment (TSM) and ground reaction force (ISGRF and ISTSM, respectively), magnitude of the TSM, individual joint contribution to the TSM, peak trunk flexion, hip, knee, and ankle range of motion, duration in seconds, the magnitudes of activation of the extensor and flexor muscles, knee extensors: flexor co-contraction indices and isometric knee extensor peak torques. Participants also answered the WOMAC questionnaire and performed the 30-second STS test (STS30). ResultsThe OABI got up from a chair with a lower TSM magnitude in the most affected limb (p = 0.040), used greater trunk flexion amplitude (p ≤ 0.034), and presented lower isometric KET (p = 0.039) and worse self-reported pain (p = 0.011) and physical function (p = 0.015). SignificanceParticipants with unilateral and bilateral KOA differ regarding lower limb kinetics and trunk kinematics while getting up from a chair, without modification in the lower limb intersegmental coordination or symmetry regarding ground reaction force or TSM distribution.

Identification of generic drilling task phases and height effect: Coupling of kinematic and kinetic data

BackgroundThe prevention of work-related musculoskeletal disorders (MSDs) is an important issue for the health of operators, especially when the workload is heavy, such as in drilling activities. Research questionThis study aimed to propose an objective identification and description of the different phases that comprise a drilling task as well as a biomechanical and ergonomic evaluation of the subjects' overall posture during its effective part. MethodsFourteen healthy subjects performed three successive drillings at two different heights, 130 (H130) and 170 cm (H170) from the ground, of a 3 mm thick steel plate. Kinematic and kinetic data were simultaneously acquired using a Qualisys motion capture system and a force platform. The speed profiles of each body segments and the evolution of the force exerted were analysed to identify the different phases. Then, the average joint angles of the whole body were calculated during the drilling phase for the two heights considered and compared. Finally, the measured postures were qualified through the Rapid Upper Limb Assessment (RULA) score in order to assess the risk of developing MSDs for each condition. ResultsThe drilling task could be divided into five phases whatever the condition: transport, aiming, repositioning, drilling, and return. The increase in height has doubled the duration of the drilling phase while reducing the force exerted by about 30 %. Similarly, height variation significantly influenced the subjects' posture, mainly in the head, trunk and upper limbs, and the RULA scores obtained for conditions H130 and H170 were 6 and 7 respectively. SignificanceThe results indicate, on the one hand, the relevance of coupling kinematic and kinetic data in order to analyse the drilling task and, on the other hand, that operators are exposed to considerable risk of developing MSDs, even at intermediate heights, which increase as the height increases.

Evaluation of a Passive Upper-Limb Exoskeleton Applied to Assist Farming Activities in Fruit Orchards

Work-related musculoskeletal disorder (WMSD) is a common occupational injury. Among the occupational injuries of agricultural workers, 93% are related to WMSD, with the shoulder being the second most affected area. This paper presents a passive upper-limb exoskeleton (PULE) with a gas spring and four-bar mechanism developed to aid the daily activities associated with orchard farming. The PULE is used to assist the arm-lifting process, reducing the physical exertion of farmers and the risk of developing WMSD. Electromyography (EMG) measurements of 26 participants were obtained to evaluate the difference in physical exertion with and without the PULE. Two arm activities: fruit thinning, with the arms raised and maintained at 100°, and pesticide spraying, with the hands swinging from 0° to 100° and back, were simulated. Using the PULE decreased muscle tension of the anterior deltoid (AD) by 17.64–19.86%. The PULE also decreased the AD activity by 37.67–39.57% during the actual orchard farming operations. The Qualisys motion capture system indicated that the difference in the lifting angle of the upper limb with and without the PULE was less than 1° and not significant (α > 0.05). Thus, the PULE did not affect the flexibility of the wearer in orchard farming activities.

Sensitivity Based Selection of an Optimal Cable-Driven Parallel Robot Design for Rehabilitation Purposes

This paper deals with the design of an optimal cable-driven parallel robot (CDPR) for upper limb rehabilitation. The robot’s prescribed workspace is identified with the help of an occupational therapist based on three selected daily life activities, which are tracked using a Qualisys motion capture system. A preliminary architecture of the robot is proposed based on the analysis of the tracked trajectories of all the activities. A multi-objective optimization process using the genetic algorithm method is then performed, where the cable tensions and the robot size are selected as the objective functions to be minimized. The cables tensions are bounded between two limits, where the lower limit ensures a positive tension in the cables at all times and the upper limit represents the maximum torque of the motor. A sensitivity analysis is then performed using the Monte Carlo method to yield the optimal design selected out of the non-dominated solutions, forming the obtained Pareto front. The robot with the highest robustness toward the disturbances is identified, and its dexterity and elastic stiffness are calculated to investigate its performance.

Moderate movement variability is optimal in massive practiced dart throws

Background and Study Aim. Movement variability is one of the fundamental topics concerning the control of human movement. In recent years, researches have focused on various aspects of variability, which has changed the noise to useful variable on human movement. Present study investigated movement variability level in high skilled dart players that repeated throws over many years.
 Material and Methods. Seven experienced dart players (three women and four men) were threw 36 darts in three sets (each set 12 throws) from a standard distance (2.37 meters), while the kinematic features of the shoulder, elbow, and wrist were recorded during the throws. Qualisys motion capture system with six cameras was used to record the kinematics of the elbow.
 Results: entropy analysis revealed that greater variability in movement angle, velocity and acceleration resulted in better dart throwing performance but after reach to this level, throw variability was decreased. The remarkable point in these findings was that variability was constant across all samples despite the varied range of experience in throwing darts from 2.37 meters distance. Entropy analysis showed that in the throws of highly experienced individuals, variation led to greater throwing efficiency.
 Conclusions: these findings suggest that variability in a throwing activity, which revealed that moderate movement variability results in optimal throwing performance when dart throw has massive amount of practice during many years.

The effects of joint hypermobility syndrome on the kinematics and kinetics of the vertical jump test

PurposeBiomechanical impairments are not apparent during walking in people with Joint Hypermobility Syndrome (JHS). This research explored biomechanical alterations during a higher intensity task, vertical jumping. Materials and methodsThis cross-sectional study compared a JHS group (n = 29) to a healthy control group (n = 30). Joint kinematics and kinetics were recorded using a Qualisys motion capture system synchronized with a Kistler platform. Independent sample t-tests and standardised mean differences (SMD) were used for statistical analysis. ResultsNo significant statistical or clinical differences were found between groups in joint kinematics and jump height (p ≥ 0.01). Sagittal hip and knee peak power generation were statistically lower in the JHS group during the compression phase (p ≤ 0.01), but not clinically relevant (SMD < 0.5). Clinically relevant reductions were found in the JHS group knee and ankle peak moments during the compression phase, and hip and knee peak power generation during the push phase (SMD ≥ 0.5), although these were not statistically significant (p ≥ 0.01). ConclusionThe JHS group achieved a similar jump height but with some biomechanical alterations. Further understanding of the joint biomechanical behavior could help to optimize management strategies for JHS, potentially focusing on neuromuscular control and strength/power training.

An Asian-centric human movement database capturing activities of daily living

Assessment of human movement performance in activities of daily living (ADL) is a key component in clinical and rehabilitation settings. Motion capture technology is an effective method for objective assessment of human movement. Existing databases capture human movement and ADL performance primarily in the Western population, and there are no Asian databases to date. This is despite the fact that Asian anthropometrics influence movement kinematics and kinetics. This paper details the protocol in the first phase of the largest Asian normative human movement database. Data collection has commenced, and this paper reports 10 healthy participants. Twelve tasks were performed and data was collected using Qualisys motion capture system, force plates and instrumented table and chair. In phase two, human movement of individuals with stroke and knee osteoarthritis will be captured. This can have great potential for benchmarking with the normative human movement captured in phase one and predicting recovery and progression of movement for patients. With individualised progression, it will offer the development of personalised therapy protocols in rehabilitation.

SteadEye-Head-Improving MARG-Sensor Based Head Orientation Measurements Through Eye Tracking Data.

This paper presents the use of eye tracking data in Magnetic AngularRate Gravity (MARG)-sensor based head orientation estimation. The approach presented here can be deployed in any motion measurement that includes MARG and eye tracking sensors (e.g., rehabilitation robotics or medical diagnostics). The challenge in these mostly indoor applications is the presence of magnetic field disturbances at the location of the MARG-sensor. In this work, eye tracking data (visual fixations) are used to enable zero orientation change updates in the MARG-sensor data fusion chain. The approach is based on a MARG-sensor data fusion filter, an online visual fixation detection algorithm as well as a dynamic angular rate threshold estimation for low latency and adaptive head motion noise parameterization. In this work we use an adaptation of Madgwicks gradient descent filter for MARG-sensor data fusion, but the approach could be used with any other data fusion process. The presented approach does not rely on additional stationary or local environmental references and is therefore self-contained. The proposed system is benchmarked against a Qualisys motion capture system, a gold standard in human motion analysis, showing improved heading accuracy for the MARG-sensor data fusion up to a factor of 0.5 while magnetic disturbance is present.

Gait biomechanics in joint hypermobility syndrome: a spatiotemporal, kinematic and kinetic analysis.

Joint hypermobility syndrome (JHS) symptoms of widespread joint hypermobility and pain, muscle weakness and reduced muscle-tendon stiffness suggest that there may be an impact on gait parameters. Identification of gait abnormalities may inform assessment and management. The objective in the present study was to use a cross-sectional designed study to explore the impact of JHS on gait parameters. A JHS group of 29 participants (mean age 37.57 (S.D. 13.77) years) was compared to a healthy control group of 30 participants (mean 39.27 (S.D. 12.59) years). Spatiotemporal parameters, joint kinematics and joint kinetics were captured using the Qualisys motion capture system synchronized with a Kistler force platform. Statistically significant reductions in walking speed, stride length and step length were found in the JHS group, while stance and double support durations were significantly increased (p < 0.01). During the swing phase, the JHS group showed significantly less knee flexion (p < 0.01). Reductions in hip extensor moment, and knee power generation and absorption were identified in the JHS group (p < 0.01). No other gait parameters were significantly altered. The JHS group walked more slowly with a kinematic 'stiffening' pattern. Hypermobility was not evident during gait. The observed stiffening pattern could be a strategy to avoid pain and improve balance. Impairments in moment and power generation could be related to several symptomatic and etiological factors in JHS. Clinicians should carefully consider gait in the assessment and management of people with JHS targeting the impairments identified by the current study.

Кривизна кривой как показатель оптимальности траектории движения в физической реабилитации. Эллиптические реабилитационные движения

The movement dynamic characteristics are the main parameters for physical exercise dosing during the athlete recovery process. However, taking into account the geometric characteristics of movement is no less important, especially when restoring the joint range of motion. The hypothesis of the study was the assumption that the use of movements’ geometric characteristics allows to “design” the optimal physiological rehabilitation patterns for movement volume restoration. Objective: to develop general principles and to create a mathematical model of the optimal trajectory characteristics for the restored part of the athlete’s musculoskeletal system. Materials and methods: We used 3D Qualisys Motion Capture and Analysis System in our investigation. The study involved 32 complex coordination sports athletes (age 9-15) with hip and ankle joint injuries (bruises, sprains strains). All they required a joint movement volume restoration. Results: The study revealed that joint movement volume restoration following the individually selected pathways involving effective mathematical modeling (study group) takes shorter time to restore the athletes than traditional physiotherapy methods (control group). For typical injuries (bruises, sprains and strains) of the hip joint area, the rehabilitation took 18±5 days for controls and 12±3 days for experimental group subjects. Nearly the same pattern was observed in restoration the ankle joint (12±4 days of recovery for controls versus 8±3 days for the experimental group). Conclusions: Restoring the joint movement volume, the workloads should be evaluated with geometric rather than dynamic indicators; for planar movement, that should be the distal limb path curvature relative to the restored joint.

A Biomechanical Analysis of Various Push-Up Positions Based on Hand Width

This study analyzed the biomechanical difference of three different push-up hand width positions: narrow, normal, and wide. A Qualisys (Göteborg, Sweden) motion capture system and in-floor AMTI (Watertown, MA, USA) force plates were used to record participants’ movements. The movement data was transferred to MATLAB and used to find the elbow flexion angle, shoulder dip ankle, spine angle, and ground reaction force (GRF) of each participant, and to make comparisons between the three push-up variations. Statistical analysis suggested that there was a statistically significant difference between push-up variants with respect to elbow flexion angle, spine angle, and shoulder dip angle, but the difference in GRF between variants was not found to be statistically significant. Measuring these factors provided insight into typical push-up posture for both men and women.

Gait quantification and visualization for digital healthcare

Gait abnormalities are common in clinical practice and there is a global imperative to improve technologies that facilitate their detection, evaluation, monitoring and management. Real time evaluation using digital technology supports the development of digital healthcare. Currently gait assessment relies on visual observation of structured clinical tests such as the “Timed Get up and Go Test.” Gold standard methods such as “Qualisys Motion Capture System” require sophisticated equipment in gait laboratories. These are not widely available due to expense, analysis time and requirement of trained technicians. Developing low cost, portable, easy to use digital technology is important to enable sophisticated assessment of gait at home or in clinics. Common measures for quantification of gait include symmetry angle, ratio and index. These measurements may be difficult to interpret by users as stand-alone values. To facilitate the evaluation and interpretation of locomotive information, a tool to visualize gait in real-time is proposed. The proposed tool consists of five approaches (1: Real-time dial visualization, 2: Visualization of individual leg time variation, 3: Visualization of both legs asymmetry, 4: Boxplot visualization, and 5: Evaluation considering all features). Results show that wearable Inertial Measurement Unit (IMU) can be used for extraction of objective gait features. This system opens possibilities for home-based assessment of gait without the requirement and expense of an elaborate laboratory setup and supports the development of digital healthcare.

Experimental and numerical investigation of a polypropylene orthotic device for assistance in level ground walking.

This study investigates the use of an orthotic device for improving pathologic gait lacking a heel-strike and its effect on the joint loads. The orthosis is fabricated from 10-mm thick polypropylene sheets joined together using a bolted joint. The gait trials are recorded using a Qualisys motion capture system and Kistler's force platform. The data recorded in this study comprise five male and five female participants, executing level ground gait under barefoot, shod and orthotic conditions. Computed tomography reconstructed foot bone-tissue model and computer-aided design model of the orthosis are used to predict the mechanical behaviour with and without orthosis under static loading. A one-way analysis of variance is conducted to compare the peak gait parameters in the early and late stance phase between the three walking conditions. The experimental results show that the orthosis reduces the peak joint forces and the rate of change of moment at the hip, knee and ankle joints. The finite element analysis results present a decrease in foot plantar pressure from 0.74 to 0.32 MPa with orthotic usage. The results of this study indicate that the orthosis can eliminate the heel-ground gap while retaining sufficient ankle motion and providing peak joint force reduction.

Predictable real-time constraints reveal anticipatory strategies of coupled planning in a sequential pick and place task.

Planning a sequence of two motor elements is much more than concatenating two independent movements. However, very little is known about the cognitive strategies that are used to perform fluent sequences for intentional object manipulation. In this series of studies, the participants' task was to reach for and pick to place a wooden cylinder to set it on a place pad of three different diameters, which served to modify terminal accuracy constraints. Participants were required to perform the sequences (1) at their preferred speed or (2) as fast as possible. Action kinematics were recorded with the Qualisys motion-capture system in order to implement a real-time protocol to get participants to engage in a true interactive relation. Results revealed that with low internal constraints (at preferred speed), low coupling between the two elements of the motor sequence was observed, suggesting a step-by-step planning strategy. Under high constraints (at fastest speed), an important terminal accuracy effect back propagated to modify early kinematic parameters of the first element, suggesting strong coupling of the parameters in an encapsulated planning strategy. In Studies 2 and 3, we further manipulated instructions and timing constraints to confirm the importance of time and predictability of external information for coupled planning. These findings overall sustain the hypothesis that coupled planning can take place in a pick and place task when anticipatory strategies are possible. This mode of action planning may be the key reason why motor intention can be read through the observation of micro variations in body kinematics.

Body weight supported treadmill vs. overground gait training for acute stroke gait rehabilitation.

The purpose of this study was to evaluate the clinical efficacy of body weight supported treadmill training for acute post-stroke rehabilitation, relative to conventional therapy. Forty individuals were randomized to receive either body weight supported treadmill training or conventional therapy as part of standard care at an acute rehabilitation facility. As part of normal care patients were evaluated using the Functional Independence Measure; gait units and length of stay were also recorded. Within 48 hours of discharge, participants were evaluated using a Qualisys motion capture system to measure spatiotemporal gait parameters. Participants allocated to the body weight supported treadmill training group had a significantly lower admission Functional Independence Measure, but had a longer length of stay, and did not have significantly different discharge Functional Independence Measure scores. Gait speed was the only spatiotemporal outcome that was significantly different at discharge, and was lower for the body weight supported treadmill training group. As seen in previous literature, the clinical efficacy of body weight supported treadmill training seems to be similar to that of conventional overground therapy. Accounting for difference in admission scores the body weight supported treadmill training and conventional therapy groups, both methods performed comparably.

Effect of Previous Groin Pain on Sagittal Plane Joint Moments During Soccer Instep Kicks

Previous groin pain is common in male soccer players, often results in re-injury,1,2 has been linked to maximal instep kicks.3,4 Research has shown aberrant kinematics during the instep kick in players with previous groin pain.5 PURPOSE: To quantify differences in sagittal plane joint moments during maximal instep kicks between players with and without previous groin pain. METHODS: Data were collected from 12 experienced male soccer players who reported nonspecific groin pain in the last 12 months, and 11 controls who each performed six maximal instep kicks. A 10-camera Qualisys motion capture system (500 Hz) and two Bertec force platforms (2000Hz.) collected data that were then processed using standard software (Visual 3D). Bilateral normalized joint moments of the hip, knee, and ankle were quantified at stance limb plant (PL), swing limb peak knee flexion (PKF) and at ball contact (BC). The foot speed of the swing limb at impact was considered an indication of kicking performance. The two-tailed alpha level was set to 0.05 and Cohen’s d was used to quantify the magnitude of differences between groups. RESULTS: A moderate difference in foot velocity existed between the groups (C: 15.5 m·s-1, PGP 14.8 m·s-1, p=0.087, D=0.77). Differences in stance limb joint moments were evident throughout the kick, while the swing limb only displayed differences at BC (Figure 1). CONCLUSION: The PGP group often utilized lower sagittal plane joint moments about the hip, knee, and ankle of the stance limb but without evidence of a matching decrease in foot velocity at BC. This suggests that compensations occurred elsewhere in the kinetic chain to make up for the reduced joint moments. The stance hip flexion moment in the PGP group at PL is atypical and further supports the presence of aberrant motor patterns. 1Walden, M. BJSM,2Werner, J. BJSM,3Rahnama, N. BJSM,4Esteve, E. BJSM,5Severin, AC. SMF.Figure 1: Graphs of joint moments of the limbs during the phases of the kick for C (black) and PGP (gray) groups. * indicates P<0.05. a indicate D>0.8, b indicate 0.5>D>0.8, and c indicate D>0.5

HEAD-TOE DISTANCE AS A SIMPLE MEASURE TO EVALUATE AMPLITUDE OF CIRCLES ON POMMEL HORSE

To develop scientifically-valid tools to monitor performance in practice, a critical question is what to measure. On pommel horse, the importance of fundamental skills called circles is uncontroversial, and one of the key performance qualities of circles is the amplitude of the movement. Previous studies have used joint angles or the magnitude of a body part’s trajectory to evaluate the amplitude, but we hypothesized that the distance between two points, namely a head and toes might be substituted despite its relative simplicity. This study examined the use of Head-Toe Distance (HTD) normalized by the gymnast’s body height as a simple variable to potentially evaluate the amplitude of circles. The kinematic data of circles performed by 18 elite gymnasts were collected with a Qualisys motion capture system operating at 100 Hz. HTD and its horizontal component, HTDh, were computed along with their relationships to the outcome scores given by the official judges, as well as the other amplitude variables: the horizontal diameters of shoulder and ankle trajectories; the body flexion angle; and in the rear support position, the shoulder extension angle and the head position. The results supported HTDh, rather than HTD, for its potential usage as a single variable to evaluate the amplitude of circles. The benefits of HTDh compared to the other variables lies in its potential validity despite its relative simplicity in assessment. Because computing HTDh requires only the positional data of the head and toes, it may have greater practical applications as an evaluative tool in gymnastics.