Peak Angular Velocity Research Articles

Biomechanical Response of the Infant Head to Shaking: An Experimental Investigation.

Controversy exists regarding whether violent shaking is harmful to infants in the absence of impact. In this study, our objective was to characterize the biomechanical response of the infant head during shaking through use of an instrumented anthropomorphic test device (commonly referred to as a "crash test dummy" or surrogate) representing a human infant and having improved biofidelity. A series of tests were conducted to simulate violent shaking of an infant surrogate. The Aprica 2.5 infant surrogate represented a 5th percentile Japanese newborn. A 50th percentile Japanese adult male was recruited to shake the infant surrogate in the sagittal plane. Triaxial linear accelerometers positioned at the center of mass and apex of the head recorded accelerations during shaking. Five shaking test series, each 3-4 sec in duration, were conducted. Outcome measures derived from accelerometer recordings were examined for trends. Head/neck kinematics were characterized during shaking events; mean peak neck flexion was 1.98 radians (113 degrees) and mean peak neck extension was 2.16 radians (123 degrees). The maximum angular acceleration across all test series was 13,260 radians/sec2 (during chin-to-chest contact). Peak angular velocity was 105.7 radians/sec (during chin-to-chest contact). Acceleration pulse durations ranged from 72.1 to 168.2 ms. Using an infant surrogate with improved biofidelity, we found higher angular acceleration and higher angular velocity than previously reported during infant surrogate shaking experiments. Findings highlight the importance of surrogate biofidelity when investigating shaking.

An exploratory investigation of changes in gait parameters with age in elderly Japanese women.

BackgroundThe aim of the present study was to identify gait parameters in elderly Japanese women. 30 elderly women (65–74.9 years old) and 19 very elderly women (≥75 years old) participated in this study. A 3-dimensional (3D) motion analysis system was used to collect kinematic data, and a total of 70 gait parameters were analysed. Gait parameters included basic gait parameters, gait cycle parameters, and joints angle parameters, as well as angular velocity parameters, such as peak velocity and timing at the hip, knee, and ankle joints.ResultsOur results indicated that basic gait parameters, such as the gait cycle, peak joint angle timing, and angular velocity parameters, significantly differ between elderly and very elderly women. Delayed peak joint angle timing and angular velocity parameters occurred during critical phases throughout the gait cycle: pre-swing, initial swing, and terminal swing phases.ConclusionsSeveral gait parameters exhibited significant differences between elderly and very elderly women. The timing of the peak joint angle and angular velocity parameters are primary characteristics defining gait changes in the elderly.

A Comparative Analysis of Biomechanical Factors and Premotor Time of Body Muscles between Elite College and Amateur Baseball Players during the Baseball Batting Motion

Purpose: The aim of this study was to analyze biomechanical factors and PMT (premotor time) of bodymuscles between elite college and amateur baseball players during the baseball batting motion.Method: Kinematic and electromyographic data were obtained for 10 elite college baseball players and 10amateur baseball players who participated in this study. All motion capture data were collected at 200 Hzusing 8 VICON cameras and the PMT of muscles was recorded using a Delsys Trigno wireless system. Thepeak mean bat speed and the peak mean angular velocities of trunk, pelvis, and bat with PMT of 16 bodymuscles were computed. These kinematic and PMT data of both groups were compared by independentt-tests (p < .05).Results: The pelvis, trunk, and bat showed a sequence of angular velocity value during baseball batting.The PMTs of right tibialis anterior, left gastrocnemius, external oblique, and erector spinae were significantlydifferent between the two groups.Conclusion: The PMT of body muscles was related to the shifting of body and rotation of the pelvis andthe trunk segment, and this action can be considered the coordinated muscle activity of the lower andupper body.

Kinematic analysis of the drag flick in field hockey

Attaining high speed of the stick head and consequently of the ball is essential for successful performance of the drag flick in field hockey, but the coordination pattern used to maximise stick head speed is unknown. The kinematics of the drag flick was studied in ten elite hockey players who performed twenty shots each towards a target located 1.5 m high. A 150 Hz active marker motion analysis system was used, alongside two force plates to detect foot touchdown. Angular velocity and contribution to stick endpoint speed of upper body joints were analysed. Repeated measures ANOVA was used to compare timing of onset and peak angular velocities between joints. Participants used a kinematic pattern that was close to a proximal-to-distal sequence. Trunk axial rotation and lateral rotation towards the target, right wrist flexion and left wrist extension were the main contributors to stick endpoint speed. Coaches should emphasise trunk rotations and wrist flexion and extension movements for maximising stick head speed. Given the high level of the participants in this study, the coordination of joints motions, as reported here, can serve as a guideline for drag flick training.

Estimations of One Repetition Maximum and Isometric Peak Torque in Knee Extension Based on the Relationship Between Force and Velocity.

We aimed to investigate whether a linear regression formula based on the relationship between joint torque and angular velocity measured using a high-speed video camera and image measurement software is effective for estimating 1 repetition maximum (1RM) and isometric peak torque in knee extension. Subjects comprised 20 healthy men (mean ± SD; age, 27.4 ± 4.9 years; height, 170.3 ± 4.4 cm; and body weight, 66.1 ± 10.9 kg). The exercise load ranged from 40% to 150% 1RM. Peak angular velocity (PAV) and peak torque were used to estimate 1RM and isometric peak torque. To elucidate the relationship between force and velocity in knee extension, the relationship between the relative proportion of 1RM (% 1RM) and PAV was examined using simple regression analysis. The concordance rate between the estimated value and actual measurement of 1RM and isometric peak torque was examined using intraclass correlation coefficients (ICCs). Reliability of the regression line of PAV and % 1RM was 0.95. The concordance rate between the actual measurement and estimated value of 1RM resulted in an ICC(2,1) of 0.93 and that of isometric peak torque had an ICC(2,1) of 0.87 and 0.86 for 6 and 3 levels of load, respectively. Our method for estimating 1RM was effective for decreasing the measurement time and reducing patients' burden. Additionally, isometric peak torque can be estimated using 3 levels of load, as we obtained the same results as those reported previously. We plan to expand the range of subjects and examine the generalizability of our results.

Quantifying warfighter performance in a target acquisition and aiming task using wireless inertial sensors

An array of inertial measurement units (IMUS) was experimentally employed to analyze warfighter performance on a target acquisition task pre/post fatigue. Eleven participants (5M/6F) repeated an exercise circuit carrying 20 kg of equipment until fatigued. IMUs secured to the sacrum, sternum, and a rifle quantified peak angular velocity magnitude (PAVM) and turn time (TT) on a target acquisition task (three aiming events with two 180° turns) within the exercise circuit. Turning performance of two turns was evaluated pre/post fatigue. Turning performance decreased with fatigue. PAVMs decreased during both turns for the sternum (p < 0.001), sacrum (p = 0.007) and rifle (p = 0.002). TT increased for the sternum (p = 0.001), sacrum (p = 0.003), and rifle (p = 0.02) during turn 1, and for the rifle (p = 0.04) during turn 2. IMUs detected and quantified changes in warfighter aiming performance after fatigue. Similar methodologies can be applied to many movement tasks, including quantifying movement performance for load, fatigue, and equipment conditions.

Specialized primary feathers produce tonal sounds during flight in rock pigeons (Columba livia).

For centuries, naturalists have suggested that the tonal elements of pigeon wing sounds may be sonations (non-vocal acoustic signals) of alarm. However, spurious tonal sounds may be produced passively as a result of aeroelastic flutter in the flight feathers of almost all birds. Using mechanistic criteria emerging from recent work on sonations, we sought to: (1) identify characteristics of rock pigeon flight feathers that might be adapted for sound production rather than flight, and (2) provide evidence that this morphology is necessary for in vivo sound production and is sufficient to replicate in vivo sounds. Pigeons produce tonal sounds (700±50 Hz) during the latter two-thirds of each downstroke during take-off. These tones are produced when a small region of long, curved barbs on the inner vane of the outermost primary feather (P10) aeroelastically flutters. Tones were silenced in live birds when we experimentally increased the stiffness of this region to prevent flutter. Isolated P10 feathers were sufficient to reproduce in vivo sounds when spun at the peak angular velocity of downstroke (53.9-60.3 rad s(-1)), but did not produce tones at average downstroke velocity (31.8 rad s(-1)), whereas P9 and P1 feathers never produced tones. P10 feathers had significantly lower coefficients of resultant aerodynamic force (CR) when spun at peak angular velocity than at average angular velocity, revealing that production of tonal sounds incurs an aerodynamic cost. P9 and P1 feathers did not show this difference in CR These mechanistic results suggest that the tonal sounds produced by P10 feathers are not incidental and may function in communication.

Characterisation of the patellar tendon reflex in cerebral palsy children using motion analysis.

The patellar tendon reflex (PTR) is an important spinal reflex and an important diagnostic tool assessing neurological disturbances. Reflexes are conveniently assessed but quantifying the response can be subjective. Motion analysis is commonly used to assess gait kinematics in a variety of populations. It can be used to objectively assess the PTR with the advantage that standard technique and hammer can be used without the need for bulky apparatus or fixing the subject position. To compare the PTR in 15 cerebral palsy (CP) children with age and height matched controls. EMG reflex latency in the rectus femoris was assessed using a Noraxon 2400T unit. Knee movement latency, knee angular displacement and peak angular velocity were captured using the CODA mpx 30 system. EMG reflex latency was significantly reduced in CP compared to control limbs (13.11 versus 18.11ms; p<0.01) confirming a 'brisk' response in this population. The kinematic data found that while knee angular displacement was significantly reduced in CP (12.82° versus 20.06°; p<0.01) there was no significant difference in movement latency or peak angular velocity compared to controls. Subjective evaluation of the PTR relies mostly on change in knee angle. Using motion analysis we have confirmed a difference in this variable in CP compared to controls. We have also shown reduced reflex latency associated with a brisk reflex. Knee movement latency and peak angular velocity did not differentiate CP from normal. Further examination of the knee angular response of the PTR is warranted in CP.

Effects of external helmet accessories on biomechanical measures of head injury risk: An ATD study using the HYBRIDIII headform

Competitive cycling is a popular activity in North America for which injuries to the head account for the majority of hospitalizations and fatalities. In cycling, use of helmet accessories (e.g. cameras) has become widespread. As a consequence, standards organizations and the popular media are discussing the role these accessories could play in altering helmet efficacy and head injury risk. We conducted impacts to a helmeted anthropomorphic headform, with and without camera accessories, at speeds of 4m/s and 6m/s, and measured head accelerations, forces on the head-form skull, and used the Simulated Injury Monitor to estimate brain tissue strain. The presence of the camera reduced peak linear head acceleration (51% – 4m/s impacts, 61% – 6m/s, p<0.05). Skull fracture risk based on kinematics was always less than 1%. For 4m/s impacts, peak angular accelerations were lower (47%, p<0.05), as were peak angular velocities (14%) with the velocity effect approaching significance (p=0.06), with the camera accessory. For 6m/s impacts, accelerations were on average higher (5%, p>0.05) as were velocities (77%, p<0.05). Skull forces were never greater than 443.2N, well below forces associated with fracture. Brain tissue strain, the cumulative strain damage measure at 25% (CSDM-25), was lower (56%, p<0.05) in 4m/s but higher (125%, p>0.05) in 6m/s impacts with the camera accessory. Based on CSDM-25 for 4m/s tests, the risk of severe concussion was reduced (p<0.05) from 25% (no camera) to 7% (camera). For 6m/s tests, risks were on average increased (p>0.05) from 18% (no camera) to 58% (camera).

Repeated Kicking Actions in Karate: Effect on Technical Execution in Elite Practitioners.

Training in martial arts is commonly performed by repeating a technical action continuously for a given number of times. This study aimed to investigate if the repetition of the task alters the proper technical execution, limiting the training efficacy for the technical evaluation during competition. This aim was pursued analyzing lower-limb kinematics and muscle activation during repeated roundhouse kicks. Six junior karate practitioners performed continuously 20 repetitions of the kick. Hip and knee kinematics and sEMG of vastus lateralis, biceps (BF), and rectus femoris were recorded. For each repetition, hip abduction-adduction and flexion-extension and knee flexion-extension peak angular displacements and velocities, agonist and antagonist muscle activation were computed. Moreover, to monitor for the presence of myoelectric fatigue, if any, the median frequency of the sEMG was computed. All variables were normalized with respect to their individual maximum observed during the sequence of kicks. Linear regressions were fitted to each normalized parameter to test its relationship with the repetition number. Linear-regression analysis showed that, during the sequence, the athletes modified their technique: Knee flexion, BF median frequency, hip abduction, knee-extension angular velocity, and BF antagonist activation significantly decreased. Conversely, hip flexion increased significantly. Since karate combat competitions require proper technical execution, training protocols combining severe fatigue and technical actions should be carefully proposed because of technique adaptations. Moreover, trainers and karate masters should consider including specific strength exercises for the BF and more generally for knee flexors.

Biomechanics of the ski cross start indoors on a customised training ramp and outdoors on snow

An effective start enhances an athlete's chances of success in ski cross competitions. Accordingly, this study was designed to investigate the biomechanics of start techniques used by elite athletes and assess the influence of different start environments. Seven elite ski cross athletes performed starts indoors on a custom-built ramp; six of these also performed starts on an outdoor slope. Horizontal and vertical forces were measured by force transducers located in the handles of the start gate and a 12-camera motion capture system allowed monitoring of the sagittal knee, hip, shoulder, and elbow kinematics. The starting movement involved Pre, Pull, and Push phases. Significant differences between body sides were observed for peak vertical and resultant forces, resultant impulse, and peak angular velocity of the shoulder joint. Significantly lower peak vertical forces (44 N), higher resultant impulse (0.114 Ns/kg), and knee joint range of motion (12°) were observed indoors. Although movement in the ski cross start is generally symmetrical, asymmetric patterns of force were observed among the athletes. Two different movement strategies, i.e. pronounced hip extension or more accentuated elbow flexion, were utilised in the Pull phase. The patterns of force and movement during the indoor and outdoor starts were similar.

Does long-distance walking improve or deteriorate walking stability of transtibial amputees?

BackgroundFalls are common in transtibial amputees which are linked to their poor stability. While amputees are encouraged to walk more, they are more vulnerable to fatigue which leads to even poorer walking stability. The objective of this study was to evaluate the dynamic stability of amputees after long-distance walking. MethodsSix male unilateral transtibial amputees (age: 53 (SD: 8.8); height: 170cm (SD: 3.4); weight: 75kg (SD: 4.7)) performed two sessions (30minutes each) of treadmill walking, separated by a short period of gait tests. Gait tests were performed before the walking (baseline) and after each session of treadmill walking. Gait parameters and their variability across repeated steps at each of the three conditions were computed. FindingsThere were no significant differences in walking speed, step length, stance time, time of occurrence, and magnitude of peak angular velocities of the knee and hip joint (P>0.05). However, variability of knee and hip angular velocity after 30-minute walking was significantly higher than the baseline (P<0.05) and after a total of 60-minute walking (P<0.05). The variability of lateral sway velocity after 30-minute walking was significantly higher than the baseline (P<0.05). InterpretationThe significant increase in variability after 30-minute walking could indicate poorer walking stability when fatigue was developed, while the significant reduction after 60-minute walking might indicate the ability of amputees to restore their walking stability after further continuous walking.

Kinematics of Overhead Throwing Motions in Professional Lacrosse and Baseball Players

There are possible kinematic similarities between the lacrosse shot and a baseball pitch, including high rotational velocities of the pelvis, torso and upper extremity and the timing of key events in a throw. PURPOSE: To compare kinematics of overhead throwing motion in professional lacrosse (LAX) players and baseball (BB) pitchers. METHODS: Three dimensional motion capture system was used to collect overhead throwing motion of LAX and BB players (N=9) in sagittal, frontal and transverse planes. The throwing cycle was defined as the time from lead foot contact (FC; 0% of throw) to the ball release (BR; 100% of throw)]. Pelvis, torso, shoulder and crosse angular velocities were determined. Joint and trunk angles at FC and BR were calculated. The range of motion (ROM) during the throw cycle of the different joint and segment motions were found. The ‘X-Factor’, was calculated as the angle of shoulder to pelvis crossover. RESULTS: Trunk lean at BR (LAX=21°±4° vs. BB=35°±5°) and trunk lean ROM (LAX=105°±13° vs. BB=38°±6°) were different between the two sports (both p<.001). Transverse ROM of the pelvis was greater in LAX than BB (LAX= 80±11 vs. BB= 46±7; p<.001). The X-Factor value at FC (LAX=-38°±10° vs. BB=-57°±10°) and at BR (LAX= 10°±7° vs. BB= 19°±11°) were both greater in BB (p<.05). Peak angular velocities of the pelvis in BB were reached at an earlier time in the throwing cycle than in LAX (BB= 10%±36% vs. LAX=44%±17%; p<.017). CONCLUSION: Different motion strategies are performed in the two sports to achieve the same result of fast ball speed. LAX players take shorter strides before FC but need to increase pelvis ROM during the initial part of the throw. But, BB players engage the pelvis earlier in the throw and increase the X-factor values at FC and BR compared to LX players to compensate for shorter lever arm before BR. These preliminary findings suggest the importance of pelvis rotation and segmental crossover during a BB throw.

Another day, another tennis coaching intervention, but does this one do what coaches purport?

A proficient serve is critical to successful tennis performance, and consequently coaches and players devote considerable time refining this stroke. In so doing, a wide variety of interventions are used or trialled, generally with very little empirical support. This study examined the efficacy of a commonly used service intervention, where players focus on exaggerating their finish (arabesque) position to promote specific changes in lower limb and trunk kinematics. The kinematics of eight high-performance junior players hitting flat serves were compared to the acute changes in kinematics elicited by the arabesque follow through position on serves using a 10-camera VICON MX motion analysis system. The significantly greater front (landing leg) hip flexion (p < 0.05) and forward trunk flexion (p < 0.05) confirmed the more exaggerated arabesque landing position following the arabesque instruction. The arabesque instruction resulted in increased frontal plane trunk range of motion and peak angular velocity in the forward swing, and increased leg drive during the drive phase. Practically, the results support the use of the arabesque instruction, effectively promoting the desired acute changes in trunk kinematics (i.e. increased frontal plane trunk rotation angular velocity) and leg drive (i.e. increased back knee extension angular velocity and front/back vertical hip velocity).

Age and sex differences in ranges of motion and motion patterns

This study investigated the effects of age and sex on joint ranges of motion (ROMs) and motion patterns. Forty participants performed 18 motions using eight body segments at self-selected speeds. Older subjects showed smaller ROMs than younger subjects for 11 motions; the greatest difference in ROM was 44.9% for eversion/inversion of the foot. Older subjects also required more time than younger subjects to approach the peak angular velocity for six motions. In contrast, sex significantly affected ROMs but not motion patterns. Male subjects exhibited smaller ROMs than female subjects for four motions; the greatest sex-dependent difference in ROM was 29.7% for ulnar/radial deviation of the hand. The age and sex effects depended on the specific segments used and motions performed, possibly because of differences in anatomical structures and frequencies of use of the joints in habitual physical activities between the groups.

Impaired anticipatory postural adjustments due to experimental infrapatellar fat pad pain.

Anticipatory postural adjustments (APAs) are motor responses generated to stabilize balance prior to voluntary movement. This study investigated how infrapatellar fat pad pain induces reorganization of APAs during reaction time tasks. It has been hypothesized that knee pain may cause insufficient APAs, thereby impairing the balance. While standing, 12 healthy men performed two reaction time tasks (shoulder flexion of the dominant side and bilateral heel lift, respectively) before, during and after experimental infrapatellar fat pad pain induced in the dominant side by injections of hypertonic saline. Isotonic saline was injected as control. The reaction time task performance was assessed by peak angle and peak angular velocity. Timing and intensity of the postural muscle activity were recorded by surface electromyography. The reaction time task performance was not significantly affected by experimental pain. The onset of muscle activity in vastus medialis, vastus lateralis and tibialis anterior muscles on the dominant side during the bilateral heel lift task was significantly delayed during pain, and their muscle activity was reduced when compared with non-painful sessions (p<0.05). The contralateral vasti muscles demonstrated early onset during pain compared with the non-painful session of the same task (p≤0.05). This study demonstrates that knee pain reorganizes the APAs which may destabilize the balance control. The knee pain-related reorganization of postural muscle activity during APA may be a part of the central modulation to maintain posture and protect the painful limb while preserving the reaction task movement performance.

Measurement of Head Impact Due to Standing Fall in Adults Using Anthropomorphic Test Dummies.

The kinematics and kinetics of head impact due to a standing fall onto a hard surface are summarized. Head injury due to impact from falls represents a significant problem, especially for older individuals. When the head is left unprotected during a fall, the impact severity can be high enough to cause significant injury or even death. To ascertain the range of head impact parameters, the dynamic response was captured for the pedestrian version of the 5th percentile female and 50th percentile male Hybrid III anthropomorphic test dummies as they were dropped from a standing position with different initial postures. Five scenarios of falls were considered including backward falls with/without hip flexion, forward falls with/without knee flexion and lateral falls. The results show that the head impact parameters are dependent on the fall scenario. A wide range of impact parameters was observed in 107 trials. The 95% prediction interval for the peak translational acceleration, peak angular acceleration, peak force, impact translational velocity and peak angular velocity are 146-502 g, 8.8-43.3 krad/s(2), 3.9-24.5 kN, 2.02-7.41 m/s, and 12.9-70.3 rad/s, respectively.

Taping of the elbow extensor muscle in chronic stroke patients: comparison between before and after three-dimensional motion analysis.

[Purpose] This study aimed to observe the effect of kinesio taping on the quality of movement of each arm during a reaching task in patients with right-sided hemiparetic stroke. [Subjects and Methods] Sixteen right-handed participants who had had a right-sided hemiparetic stroke were requested to perform a reaching task with each arm, with and without kinesio taping. A three-dimensional motion analysis system was used to measure peak angular velocity, time to reach peak angular velocity, and movement units during elbow motion. [Results] In the right arm, movements during the reaching task with kinesio taping were faster, smoother, and more efficient than those without kinesio taping. The peak angular velocity increased, and the time to reach peak angular velocity decreased. Movement units decreased significantly. However, in the untaped arm, the movement was slower, rougher, and less efficient. [Conclusion] Kinesio taping provided a positive effect on the reaching movement of the taped arm of right-handed persons who had had a right-sided hemiparetic stroke.

A kinematic comparison of the overhand throw and tennis serve in tennis players: How similar are they really?

Tennis coaches often use the fundamental throwing skill as a training tool to develop the service action. However, recent skill acquisition literature questions the efficacy of non-specific training drills for developing complex sporting movements. Thus, this study examined the mechanical analogy of the throw and the tennis serve at three different levels of development. A 500 Hz, 22-camera VICON MX motion capture system recorded 28 elite female tennis players (prepubescent (n = 10), pubescent (n = 10), adult (n = 8)) as they performed flat serves and overhand throws. Two-way ANOVAs with repeated measures and partial correlations (controlling for group) assessed the strength and nature of the mechanical associations between the tasks. Preparatory mechanics were similar between the two tasks, while during propulsion, peak trunk twist and elbow extension velocities were significantly higher in the throw, yet the peak shoulder internal rotation and wrist flexion angular velocities were significantly greater in the serve. Furthermore, all of these peak angular velocities occurred significantly earlier in the serve. Ultimately, although the throw may help to prime transverse trunk kinematics in the serve, mechanics in the two skills appear less similar than many coaches seem to believe. Practitioners should, therefore, be aware that the throw appears less useful for priming the specific arm kinematics and temporal phasing that typifies the tennis serve.

Agonist and antagonist muscle activation in elite athletes: influence of age.

Age-related neuromuscular control adaptations have been investigated mainly in untrained populations, where higher antagonist activation in adults was observed with respect to children. In elite athletes age-related differences in neuromuscular control have scarcely been investigated. Therefore, this study aims at investigating differences in co-activation about the knee joint in two groups of karate athletes belonging to the Junior (JK) and Senior (SK) age categories, performing the roundhouse kick (RK). Six SK and six JK performed the RK impacting on a punching bag. Each participant performed three attempts during which kicking limb kinematics and sEMG from the vastus lateralis (VL) and from the biceps femoris (BF) were recorded. Co-activation index during knee flexion and extension (CIF; CIE) and agonist and antagonist activation areas of VL and BF (I AGO-VL; I AGO-BF; I ANT-VL; I ANT-BF) were computed. Hip and knee range of motion, peak angular velocity and minima and maxima of lower limb angular momentum were computed. During knee extension, the SK demonstrated higher CIE, higher IANT-BF and higher total angular momentum with respect to the JK. Significant relationships were observed between I ANT-BF and total angular momentum maxima, and between I ANT-BF and age. IANT-BF is partially related to the age of the group and to joint protection upon impact. Moreover, given the very brief duration of the task, a feed-forward mechanism modulating antagonist activation partly based on the stress imposed on the knee joint could be hypothesized. This mechanism potentially involves skill dependent re-modelling of the peripheral and central nervous system.