Peak Trunk Velocity Research Articles

Pain Education and Virtual Reality Improves Pain, Pain-related Fear of Movement, and Trunk Kinematics in Individuals With Persistent Low Back Pain.

To evaluate the effect of combining pain education and virtual reality (VR) exposure therapy using a cognitive-behavioral therapy-informed approach (virtual reality-based cognitive behavioral therapy [VR-CBT]) on pain intensity, fear of movement, and trunk movement in individuals with persistent low back pain. Thirty-seven participants were recruited in a single cohort repeated measures study, attending 3 sessions 1 week apart. The VR-CBT intervention included standardized pain education (session 1) and virtual reality-based exposure therapy (VRET; session 2) incorporating gameplay with mixed reality video capture and reflective feedback of performance. Outcome measures (pain intensity, pain-related fear of movement (Tampa Scale of Kinesiophobia), and trunk kinematics during functional movements (maximum amplitude and peak velocity) were collected at baseline (session 1) and 1 week after education (session 2) and VRET (session 3). One-way repeated measures analysis of variances evaluated change in outcomes from baseline to completion. Post hoc contrasts evaluated effect sizes for the education and VR components of VR-CBT. Thirty-four participants completed all sessions. Significant ( P < 0.001) reductions were observed in mean (SD) pain (baseline 5.9 [1.5]; completion 4.3 [2.1]) and fear of movement (baseline 42.6 [6.4]; completion 34.3 [7.4]). Large effect sizes (Cohen d ) were observed for education (pain intensity: 0.85; fear of movement: 1.28), whereas the addition of VRET demonstrated very small insignificant effect sizes (pain intensity: 0.10; fear of movement: 0.18). Peak trunk velocity, but not amplitude, increased significantly ( P < 0.05) across trunk movement tasks. A VR-CBT intervention improved pain, pain-related fear of movement, and trunk kinematics. Further research should explore increased VR-CBT dosage and mechanisms underlying improvement.

Kinematic, Kinetic, and Temporal Metrics Associated With Golf Proficiency.

McHugh, MP, O'Mahoney, CA, Orishimo, KF, Kremenic, IJ, and Nicholas, SJ. Kinematic, kinetic, and temporal metrics associated with golf proficiency. J Strength Cond Res 38(3): 599-606, 2024-The biomechanics of the golf swing have been studied extensively, but the literature is unclear on which metrics are indicative of proficiency. The purpose of this study was to determine which metrics identified golf proficiency. It was hypothesized that discrete kinematic, kinetic, and temporal metrics would vary depending on proficiency and that combinations of metrics from each category would explain specific proficiency metrics. Kinematic, kinetic, and temporal metrics and their sequencing were collected for shots performed with a driver in 33 male golfers categorized as proficient, average, or unskilled (based on a combination of handicap, ball velocity, and driving distance). Kinematic data were collected with high-speed motion analysis, and ground reaction forces (GRF) were collected from dual force plates. Proficient golfers had greater x-factor at ball impact and greater trunk deceleration before ball impact compared with average ( p < 0.05) and unskilled ( p < 0.01) golfers. Unskilled golfers had lower x-factor at the top of the back swing and lower peak x-factor, and they took longer to reach peak trunk velocity and peak lead foot GRF compared with average ( p < 0.05) and proficient ( p < 0.05) golfers. A combination of 2 kinematic metrics (x-factor at ball impact and peak pelvis velocity), 1 kinetic metric (peak lead foot GRF), and 2 timing metrics (the timing of peak trunk and arm velocity) explained 85% of the variability in ball velocity. The finding that x-factor at ball impact and trunk deceleration identified golf proficiency points to the potential for axial trunk rotation training to improve performance.

Role of Pelvis and Trunk Biomechanics in Generating Ball Velocity in Baseball Pitching.

Orishimo, KF, Kremenic, IJ, Mullaney, MJ, Fukunaga, T, Serio, N, and McHugh, MP. Role of pelvis and trunk biomechanics in generating ball velocity in baseball pitching. J Strength Cond Res 37(3): 623-628, 2023-The purpose of this study was to determine the impact of pelvis rotation velocity, trunk rotation velocity, and hip-shoulder separation on ball velocity during baseball pitching. Fastball pitching kinematics were recorded in 29 male pitchers (age 17 ± 2 years, 23 high school, 6 college). Pelvis and trunk angular velocities and hip-shoulder separation were calculated and averaged for the 3 fastest pitches. Associations between peak pelvis velocity, peak trunk velocity, hip-shoulder separation at foot contact, and ball velocity were assessed using Pearson correlation coefficients and multiple regression. The average ball velocity was 33.5 ± 2.8 m·s -1 . The average hip-shoulder separation at foot contact was 50 ± 12°. The peak pelvis velocity (596 ± 88°·s -1 ) occurred at 12 ± 11% of the time from stride foot contact to ball release, with the peak trunk velocity (959 ± 120°·s -1 ) occurring at 36 ± 11%. Peak trunk velocity was predictive of ball velocity ( p = 0.002), with 25% of the variability in ball velocity explained. No combination of factors further explained ball velocity. Hip-shoulder separation at foot contact (17%, p = 0.027), peak pelvis velocity (23%, p = 0.008), and the timing of peak pelvis velocity (16%, p = 0.031) individually predicted peak trunk velocity. The combination of peak pelvis velocity, hip-shoulder separation at foot contact, and the timing of peak trunk velocity explained 55% of the variability in trunk rotation velocity ( p < 0.001). These data highlight the importance of interactions between pelvis and trunk for maximizing velocity in pitching. Training to improve pelvis-trunk axial dissociation may increase maximal trunk rotation velocity and thereby increase ball velocity without increasing training load on the shoulder and elbow.

Effects of wearing a head-mounted display during a standard clinical test of dynamic balance

BackgroundThe use of virtual reality (VR) in clinical settings has increased with the introduction of affordable, easy-to-use head-mounted displays (HMDs). However, some have raised concerns about the effects that HMDs have on posture and locomotion, even without the projection of a virtual scene, which may be different across ages. Research questionHow does HMD wear impact the kinematic measures in younger and older adults? MethodsTwelve healthy young and sixteen older adults participated in two testing conditions: 1) TUG with no HMD and 2) TUG with an HMD displaying a scene of the actual environment (TUGHMD). The dependent variables were the pitch, yaw, and roll peak trunk velocities (PTVs) in each TUG component, turning cadence, and the time to complete the TUG and its components – SIT-TO-STAND, TURN, WALK, and STAND-TO-SIT. ResultsWearing the HMD decreased turning cadence and pitch and yaw PTVs in all TUG components, decreased roll PTV in SIT-TO-STAND and TURN, and increased the time taken to complete all TUG components in all participants. Wearing the HMD decreased the pitch PTV in SIT-TO-STAND in older relative to younger adults.Wearing an HMD affected TUG performance in younger and older adults, which should be considered when an HMD is used for VR applications in rehabilitation. SignificanceOur findings highlight the importance of considering the physical effect of HMD wear in clinical testing, which may not be present with non-wearable VR technologies.

Balance confidence and turning behavior as a measure of fall risk

BackgroundDiminished balance confidence increases the risk of a fall and falls that occur when turning during walking are associated with an eightfold increase in hip fractures compared to when walking in a straight trajectory. Although an effect of aging on turning is revealed, the role of gender during turning is not yet clear. Research QuestionHow can balance confidence impact turning behavior in younger, middle-aged, and older men and women? MethodsThis cross-sectional study included 22 young adults (11 women), 13 middle-aged adults (9 women), and 13 older adults (6 women). Participants ranked their balance confidence using the activities-specific balance confidence (ABC) scale and completed two different turns: Turn1 (around the cone) and Turn2 (turn to sit). Measures obtained for each turn included: turning time, step count, and peak trunk velocities (PTV) in pitch, yaw, and roll. ResultsIn Turn1, older adults exhibited an increase in turning time and step count relative to younger adults (both p < 0.03). In Turn2, older adults showed an increase in turning time and roll PTV compared to the middle-aged group (both p < 0.02). Lower scores in ABC were significantly correlated with an increase in Turn1 time (p < 0.001) and step count (p = 0.04) in middle-aged and older adults, respectively. Bivariate correlations revealed that women with lower scores on the ABC took more time to complete both turns (both p = 0.01). SignificanceOlder adults demonstrated longer turning time, more steps, and higher roll PTV while turning that were associated with decreased balance confidence scores. The association between decreased balance confidence and turning kinematics implies a relationship between turning and increased fall risk. These results suggest that testing for fall risk requires tests of activities that are performed outside traditional clinical settings and gait laboratories.

Visual dependence affects the motor behavior of older adults during the Timed Up and Go (TUG) test

BackgroundOlder adults show greater postural instabilities under misleading visual cues relative to younger adults. We investigated the effects of age-related visual dependence on motor performance under increased attention demands by adding a motor task and visual stimulus to the Timed Up and Go (TUG) test sub-components. MethodWe designed a cross-sectional quantitative study. Twenty-eight younger (n = 12) and older (n = 16) adults completed the TUG test while wearing a head-mounted display (HMD) that presented a visual stimulus and/or carrying a cup of water. Outcome measures were turning cadence; gait speed; pitch, yaw, and roll peak trunk velocities (PTVs); and acceleration ranges of sit-to-stand and stand-to-sit. ResultsWearing the HMD caused significant performance differences in the TUG test tasks due to age and visual dependence, although performance was lower across all groups with the HMD (p < 0.01). Older adults showed lower roll PTV in turning compared to younger adults (p = 0.03). Visually dependent older adults showed smaller mediolateral and vertical acceleration ranges (p < 0.04) in sit-to-stand compared to visually independent older adults. ConclusionThe demand for orienting posture to a vertical position during sit-to-stand may differentiate older adults who are more visually dependent—and thus at greater fall risk— from those who are more visually independent. Age-related differences in turning behavior suggest a relationship with fall risk that warrants further investigation.

Gait and trunk kinematics during prolonged turning in Parkinson's disease with freezing of gait

IntroductionAlthough turning during walking is known to trigger freezing of gait (FOG) in Parkinson's disease (PD), little is known about kinematic strategies used by individuals with PD and FOG while performing prolonged turning. ObjectiveOur aim was to compare gait and trunk kinematics during straight walking and continuous turning over 20-min in PD with and without FOG. Methods18 individuals with idiopathic PD (n = 9 with FOG, n = 9 without FOG), performed two 20-min walking tasks: straight ahead, and turning, in a laboratory setting in their OFF medication state. Accelerometer-based spatial and temporal gait parameters and trunk kinematics (range of motion, peak velocity, variability of range of motion and peak velocity) were analyzed. ResultsDuring turning, PD with FOG reduced cadence more compared to PD without FOG (P <0.045), despite similar decline in stride velocity (28–32%) and stride length (24–27%). Participants with FOG had decreased variability of gait speed (P <0.011), stride length (P <0.035), frontal trunk range of motion (P <0.040) and peak trunk velocity (P <0.017) compared to PD without FOG during turning, whereas there was no difference between groups during straight walking. Gait speed variability and cadence between these two tasks differentiated the PD groups (sensitivity 89% and specificity 78%). ConclusionsWe demonstrate that PD with FOG decreased cadence and reduced variability of walking speed, stride length, and lateral flexion of the trunk compared to PD without FOG during prolonged turning. These real-life gait markers are observable during lab-based gait that is similar to daily-life.

Repetitive trunk loading leads to faster trunk movement in response to external perturbation

The purpose of the present study was to examine trunk movement pattern responses to mechanical perturbation before and after two different repetitive trunk flexion-extension loading schemes. Spatial and temporal parameters were studied to understand the trunk recovery from an anteriorly directed perturbation. Eighteen male and female subjects (18–27 yrs) participated in active and passive trunk flexion-extension, performed seven days apart. Subjects performed 60 trunk flexion-extension repetitions in each condition. Subjects either volitionally moved their trunks (active condition) or relaxed while a dynamometer controlled the movements (passive condition). Trunk perturbations occurred before and immediately after two 30 repetition sessions. Initial responses included latency measures of trunk displacement and peak trunk velocity (VP). Temporal measures included perturbation onset to initial trunk movement (TD), movement initiation to VP (TMIPV), and perturbation onset to VP (TPPV). Recovery measures included peak recovery velocity (VPR), recovery time (TR), velocity slope (VS), and recovery slope (RS). Differences between loading sessions were present for TPPV (p < .05), TR (p < .05), and RS (p < .05). Overall, the results indicate repetitive loading leads to lower resistance to perturbation, but faster recovery from perturbation although no differences to active or passive repetitive loading was observed.

Fallers with Parkinson’s disease exhibit restrictive trunk control during walking

BackgroundThe relationship between falls and static and dynamic postural control has not been established in Parkinson’s disease (PD). The purpose was to compare the compensatory postural strategies among fallers and non-fallers with PD as well as older adults during static and dynamic movements. MethodsTwenty-five individuals with PD (11 fallers) and 17 older adults were outfitted with 6 accelerometers on the wrists, ankles, lumbar spine, and sternum, stood quietly for 30 s on a force platform, and walked back and forth for 30 s along a 15 m walkway. Root-mean-square displacement amplitude of the center of pressure (COP), COP velocity, gait spatial-temporal characteristics, trunk range of motion (ROM), and peak trunk velocities were obtained. ResultsCOP velocity in anterior-posterior was larger in older adults than those with PD (p < 0.05). Trunk frontal ROM and velocity were smaller in fallers and non-fallers with PD compared to older adults (p < 0.05). Trunk anterior-posterior ROM and velocity were smaller in fallers than non-fallers with PD and older adults (p < 0.05). In fallers with PD, negative correlations were shown between the sagittal trunk velocity and the COP velocity in the anterior-posterior direction as well as between trunk frontal velocity and COP velocity in both directions (p < 0.05). In non-fallers with PD, horizontal trunk ROM and velocity were positively correlated with COP ROM and velocity in the medial-lateral direction (p < 0.01). SignificanceDynamic postural control revealed better discrimination between groups than static. Fallers and non-fallers with PD and older adults adopted different compensatory strategies during static and dynamic movements; thereby providing important information for falls-risk assessment.

Effects of Head-Mounted Display on kinematics of the Timed Up and GO (TUG) test: does the addition of a visual stimulus matter?

Effects of Head-Mounted Display on kinematics of the Timed Up and GO (TUG) test: does the addition of a visual stimulus matter?

Fall risk during opposing stance perturbations among healthy adults and chronic stroke survivors.

Studies examining recovery from SLIPS and TRIPS indicate higher incidence of falls during SLIPS than TRIPS however, differences in the recovery mechanisms during these opposing perturbations have not been examined. We therefore aimed to compare the reactive balance responses contributing to fall risk during SLIPS and TRIPS at comparable perturbation intensity among community-dwelling healthy adults and chronic stroke survivors. Younger adults (N = 11), age-matched adults (N = 11) and chronic stroke survivors (N = 12) were exposed to a single SLIP and TRIP through a motorized treadmill (16m/s2, 0.20m). Center of mass (COM) state stability was measured by recording COM position and velocity relative to base of support, i.e., Ḋ COM/BOS and Ẋ COM/BOS, respectively. Trunk and compensatory step kinematics were alsorecorded. During SLIPS, the incidence of falls among stroke survivors was greater than healthy adults (53.83% vs. 0%), however not for TRIPS. All groups showed higher change in postural stability from liftoff to touchdown during TRIPS than SLIPS. Among healthy adults higher change in Ḋ COM/BOS during TRIPS was accompanied by the ability to control trunk flexion at step touchdown and lower peak trunk velocity as compared with SLIPS, with no significant differences in compensatory step length between the perturbations (p > 0.05). Chronic stroke survivors increased compensatory step length during TRIPS versus SLIPS (p < 0.05) contributing to greater stability change. They were unable to control trunk excursion and peak trunk velocity as compared with thehealthy adults leading to lower stability than healthy younger and age-matched adults during SLIPS and lower stability than younger adults during TRIPS. Difficulty in trunk control during SLIPS among all individuals and compensatory step length among stroke survivors emphasizes higher fall risk for SLIPS than TRIPS among these populations.

Trunk response to sudden forward perturbations – Effects of preload and sudden load magnitudes, posture and abdominal antagonistic activation

Unexpected loading of the spine is a risk factor for low back pain. The trunk neuromuscular and kinematics responses are likely influenced by the perturbation itself as well as initial trunk conditions. The effect of four parameters (preload, sudden load, initial trunk flexed posture, initial abdominal antagonistic activity) on trunk kinematics and back muscles reflex response were evaluated. Twelve asymptomatic subjects participated in sudden forward perturbation tests under six distinct conditions. Preload did not change the reflexive response of back muscles and the trunk displacement; while peak trunk velocity and acceleration as well as the relative load peak decreased. Sudden load increased reflex response of muscles, trunk kinematics and loading variables. When the trunk was initially flexed, back muscles latency was delayed, trunk velocity and acceleration increased; however, reflex amplitude and relative trunk displacement remained unchanged. Abdominal antagonistic preactivation increased reflexive response of muscles but kinematics variables were not affected. Preload, initial flexed posture and abdominal muscles preactivation increased back muscles preactivity. Both velocity and acceleration peaks of the trunk movement decreased with preload despite greater total load. In contrast, they increased in the initial flexed posture and to some extent when abdominal muscles were preactivated demonstrating the distinct effects of pre-perturbation variables on trunk kinematics and risk of injury.

Trunk bradykinesia and foveation delays during whole-body turns in spasmodic torticollis

We have investigated how the abnormal head posture and motility in spasmodic torticollis interferes with ecological movements such as combined eye-to-foot whole-body reorientations to visual targets. Eight mildly affected patients and 10 controls voluntarily rotated eyes and body in response to illuminated targets of eccentricities up to ±180°. The experimental protocol allowed separate evaluation of the effects of target location, visibility and predictability on movement parameters. Patients’ latencies of eye, head, trunk and foot motion were prolonged but showed a normal modification pattern when target location was predictable. Peak head-on-trunk displacement and velocity were reduced both ipsi- and contralaterally with respect to the direction of torticollis. Surprisingly, peak trunk velocity was also reduced, even more than in previously studied patients with Parkinson’s disease. As a consequence, patients made short, hypometric gaze saccades and only exceptionally foveated initially nonvisible targets with a single large gaze shift (4 % of predictable trials as opposed to 30 % in controls). Foveation of distant targets was massively delayed by more than half a second on average. Spontaneous dystonic head movements did not interfere with the execution of voluntary gaze shifts. The results show that neck dystonia does not arise from gaze (head-eye) motor centres but the eye-to-foot turning synergy is seriously compromised. For the first time we identify significant ‘secondary’ complications of torticollis such as trunk bradykinesia and foveation delays, likely to cause additional disability in patients. Eye movements per se are intact and compensate for the reduced head/trunk performance in an adaptive manner.

Trunk and upper extremity kinematics during sitting pivot transfers performed by individuals with spinal cord injury

Although reaching an optimal level of independence during sitting pivot transfer is crucial for individuals with spinal cord injury, little is known regarding the kinematic requirements of this functional task. Ten males with spinal cord injury performed independent sitting pivot transfers between an initial seat and a target one placed at same (50 cm), lower (40 cm), and higher heights (60 cm) than the initial one, using their usual movement strategies. Three-dimensional trunk, shoulder, elbow and wrist kinematics were collected bilaterally during sitting pivot transfers. Each sitting pivot transfer was divided into three phases for analysis: pre-lift, lift-pivot and post-lift. Temporal parameters were also documented. Peak shoulder extension displacement and velocities were always higher at the leading shoulder compared to the trailing one (P<0.004), and almost coincided with peak trunk velocities early during the lift phase. With increasing target seat height, shoulder flexion (P<0.011) and elbow extension (P<0.013) displacements and velocities of the trailing upper extremity augmented and reached higher values at this upper extremity compared to the leading upper extremity, with one exception at the shoulder. Elbows generally remained flexed (min=28-56 degrees ) during the lift phase of all transfers whereas extreme wrist extension positions (max=84-88 degrees ) were documented across all transfers. Total durations of transfers (2.6-2.8s) and lift-pivot phases (1.0-1.3s) were not affected by target seat heights. Sitting pivot transfers are characterized by substantial angular displacements and velocities at the trunk and upper extremities. Some kinematic parameters documented during sitting pivot transfers may increase the risk of developing secondary musculoskeletal impairments in this population.

ADAPTIVE BALANCE STRATEGIES EXHIBITED DURING GAIT BY OLDER AND YOUNGER ADULTS IN RESPONSE TO SENSORY CHALLENGES TO DYNAMIC BALANCE.

Purpose/Hypothesis: Age-related balance deficits and falls pose serious health risks for older adults. Older adults fall most often during dynamic activities such as gait, especially when surfaces are irregular or varied. Gait requires dynamic balance, the ability to maintain balance while moving, and is controlled by integration of multiple sensory and motor systems. Success with dynamic balance depends in part on an individual's ability to adapt to changing sensory environments. Knowledge is limited concerning the adaptations to movement strategies must occur for older and younger adults to maintain dynamic balance during challenges to two key sensory systems, proprioception and vision. The purpose of this study was to characterize the adaptive balance strategies older and younger adults produced during gait under conditions of single sensory challenge (proprioceptive or visual) and simultaneous proprioceptive and visual challenge. Subjects: In this 2(group) X 4(condition) factorial design study, 40 subjects (20 young/20 older adults) ambulated under 4 conditions: a level firm surface, unstable surface, firm surface with vision obscured, and unstable surface with vision obscured. Materials/Methods: Adaptation to gait was measured by changes in gait speed, stride length, cadence, and Gait Stability Ratio (GSR). Adaptation regarding head stability was measured by peak head and trunk angular velocities in three planes of motion: pitch, roll and yaw. Results: Significant main effects for gait condition were found for gait speed (p<.0001) and cadence (p<.0001). Significant main effects for the interaction of age and gait condition were found for stride length (p = .001) and GSR (p = .002). A significant main effect for condition was found for peak trunk velocity in the roll plane (p<.0001). Significant interaction effects were found for peak head velocity in pitch (p = .001), roll (p = .006) and yaw (p = .003) and for peak trunk velocity in pitch (p = .008) and yaw (p<.0001). Conclusions: Both older and younger adults adapt gait speed, cadence and lateral trunk motion under conditions that challenge sensory systems in order to assume a more stable gait. Adaptations to stride length, GSR, and peak head and trunk velocities in other planes, however, differ for older and younger adults depending on the type of sensory challenge. Older and younger adults exhibit adaptive changes to gait and head stability parameters that vary in degree as challenge increases. Under the same conditions, older adults in general show greater adaptation to gait and achieve less stability of the head in space than do young adults indicating poorer control of dynamic balance. Clinical Relevance: The results of this study add to the understanding of dynamic balance control and age-related changes in balance. This knowledge has relevance clinically in that it may improve identification of older adults with an increased risk for falling.

Coordinated turn-and-reach movements. I. Anticipatory compensation for self-generated coriolis and interaction torques.

When reaching movements involve simultaneous trunk rotation, additional interaction torques are generated on the arm that are absent when the trunk is stable. To explore whether the CNS compensates for such self-generated interaction torques, we recorded hand trajectories in reaching tasks involving various amplitudes and velocities of arm extension and trunk rotation. Subjects pointed to three targets on a surface slightly above waist level. Two of the target locations were chosen so that a similar arm configuration relative to the trunk would be required for reaching to them, one of these targets requiring substantial trunk rotation, the other very little. Significant trunk rotation was necessary to reach the third target, but the arm's radial distance to the body remained virtually unchanged. Subjects reached at two speeds-a natural pace (slow) and rapidly (fast)-under normal lighting and in total darkness. Trunk angular velocity and finger velocity relative to the trunk were higher in the fast conditions but were not affected by the presence or absence of vision. Peak trunk velocity increased with increasing trunk rotation up to a maximum of 200 degrees /s. In slow movements, peak finger velocity relative to the trunk was smaller when trunk rotation was necessary to reach the targets. In fast movements, peak finger velocity was approximately 1.7 m/s for all targets. Finger trajectories were more curved when reaching movements involved substantial trunk rotation; however, the terminal errors and the maximal deviation of the trajectory from a straight line were comparable in slow and fast movements. This pattern indicates that the larger Coriolis, centripetal, and inertial interaction torques generated during rapid reaches were compensated by additional joint torques. Trajectory characteristics did not vary with the presence or absence of vision, indicating that visual feedback was unnecessary for anticipatory compensations. In all reaches involving trunk rotation, the finger movement generally occurred entirely during the trunk movement, indicating that the CNS did not minimize Coriolis forces incumbent on trunk rotation by sequencing the arm and trunk motions into a turn followed by a reach. A simplified model of the arm/trunk system revealed that additional interaction torques generated on the arm during voluntary turning and reaching were equivalent to < or =1.8 g (1 g = 9.81 m/s(2)) of external force at the elbow but did not degrade performance. In slow-rotation room studies involving reaching movements during passive rotation, Coriolis forces as small as 0.2 g greatly deflect movement trajectories and endpoints. We conclude that compensatory motor innervations are engaged in a predictive fashion to counteract impending self-generated interaction torques during voluntary reaching movements.

Spatial and temporal control of trunk-assisted prehensile actions.

The present study utilized a trunk-assisted prehension task to examine the hypothesis that there is spatial regularity between the grasp and transport components. To test this hypothesis, we varied movement amplitude, reach speed, and object size. When examining the opening and closure phases of aperture formation, it was found that the distance to peak aperture increased systematically with hand-path trajectory length, while the distance from peak aperture to the object remained constant, which supports the notion of state-space control. Regarding the relationship among the body segments involved, temporal measures such as relative time to peak aperture, and peak velocity of the arm and trunk were altered by the changes in both object size and reach speed. It was also found that the time to peak trunk velocity was coupled with the time to peak arm velocity as well as with the time to peak aperture. Based on these results, it appears that the trunk is closely linked not only to the arm motion, but also to the aperture formation. Collectively, these findings suggest that, during trunk-assisted prehension, the arm and the trunk are coordinated by neuromotor synergies that appear to position grip aperture for a stable closure to grasp the object.

A comparison of peak vs cumulative physical work exposure risk factors for the reporting of low back pain in the automotive industry

Objective. To determine the relative importance of modelled peak spine loads, hand loads, trunk kinematics and cumulative spine loads as predictors of reported low back pain (LBP). Background. The authors have recently shown that both biomechemical and psychosocial variables are important in the reporting of LBP. In previous studies, peak spinal load risk factors have been identified and while there is in vitro evidence for adverse effects of excessive cumulative load on tissue, there is little epidemiological evidence. Methods. Physical exposures to peak and cumulative lumbar spine moment, compression and shear forces, trunk kinematics, and forces on hands were analyzed on 130 randomly selected controls and 104 cases. Univariable and multivariable odds ratios of the risk of reporting were calculated from a backwards logistic regression analysis. Interrelationships among variables were examined by factor analysis. Results. Cases showed significantly higher loading on all biomechanical variables. Four independent risk factors were identified: integrated lumbar moment (over a shift), ‘usual’ hand force, peak shear force at the level of L 4 L 5 and peak trunk velocity. Substituting lumbar compression or moment for shear did not appreciably alter odds ratios because of high correlations among these variables. Conclusions. Cumulative biomechanical variables are important risk factors in the reporting of LBP. Spinal tissue loading estimates from a biomechanical model provide information not included in the trunk kinematics and hand force inputs to the model alone. Workers in the top 25% of loading exposure on all risk factors are at about six times the risk of reporting LBP when compared with those in the bottom 25%.