Comparison of strength measurements under single-joint and multi-joint conditions in hemiparetic individuals

Ergonomic Risk Identification for Spacesuit Movements Using Factorial Analysis

OCCUPATIONAL APPLICATIONSBiomechanical risk factors associated with spacesuit manual material handling tasks were evaluated using the singular value decomposition (SVD) technique. SVD analysis decomposed each lifting tasks into primitive motion patterns called eigenposture progression (EP) that contributed to the overall task. Biomechanical metrics, such as total joint displacement, were calculated for each EP. The first EP (a simultaneous knee, hip, and waist movement) had greater biomechanical demands than other EPs. Thus, tasks such as lifting from the floor were identified as "riskier" by having a greater composition of the first EP. The results of this work can be used to improve a task as well as spacesuit design by minimizing riskier movement patterns as shown in this case study. This methodology can be applied in civilian occupational settings to analyze open-ended tasks (e.g., complex product assembly and construction) for ergonomics assessments. Using this method, worker task strategies can be evaluated quantitatively, compared, and redesigned when necessary.

Strength deficits of the shoulder complex during isokinetic testing in people with chronic stroke

OBJECTIVES

To examine the strength deficits of the shoulder complex after stroke and to characterize the pattern of weakness according to type of movement and type of isokinetic parameter.

METHOD

Twelve chronic stroke survivors and 12 age-matched healthy controls had their shoulder strength measured using a Biodex isokinetic dynamometer. Concentric measures of peak torque and work during shoulder movements were obtained in random order at speeds of 60°/s for both groups and sides. Type of movement was defined as scapulothoracic (protraction and retraction), glenohumeral (shoulder internal and external rotation) or combined (shoulder flexion and extension). Type of isokinetic parameter was defined as maximum (peak torque) or sustained (work). Strength deficits were calculated using the control group as reference.

RESULTS

The average strength deficit for the paretic upper limb was 52% for peak torque and 56% for work. Decreases observed in the non-paretic shoulder were 21% and 22%, respectively. Strength deficit of the scapulothoracic muscles was similar to the glenohumeral muscles, with a mean difference of 6% (95% CI -5 to 17). Ability to sustain torque throughout a given range of motion was decreased as much as the peak torque, with a mean difference of 4% (95% CI -2 to 10).

CONCLUSIONS

The findings suggest that people after stroke might benefit from strengthening exercises directed at the paretic scapulothoracic muscles in addition to exercises of arm elevation. Clinicians should also prescribe different exercises to improve the ability to generate force and the ability to sustain the torque during a specific range of motion.

Elastic, viscous, and mass load effects on poststroke muscle recruitment and co-contraction during reaching: a pilot study

BACKGROUND

Resistive exercise after stroke can improve strength (force-generating capacity) without increasing spasticity (velocity-dependent hypertonicity). However, the effect of resistive load type on muscle activation and co-contraction after stroke is not clear.

OBJECTIVE

The purpose of this study was to determine the effect of load type (elastic, viscous, or mass) on muscle activation and co-contraction during resisted forward reaching in the paretic and nonparetic arms after stroke.

DESIGN

This investigation was a single-session, mixed repeated-measures pilot study.

METHODS

Twenty participants (10 with hemiplegia and 10 without neurologic involvement) reached forward with each arm against equivalent elastic, viscous, and mass loads. Normalized shoulder and elbow electromyography impulses were analyzed to determine agonist muscle recruitment and agonist-antagonist muscle co-contraction.

RESULTS

Muscle activation and co-contraction levels were significantly higher on virtually all outcome measures for the paretic and nonparetic arms of the participants with stroke than for the matched control participants. Only the nonparetic shoulder responded to load type with similar activation levels but variable co-contraction responses relative to those of the control shoulder. Elastic and viscous loads were associated with strong activation; mass and viscous loads were associated with minimal co-contraction.

LIMITATIONS

A reasonable, but limited, range of loads was available.

CONCLUSIONS

Motor control deficits were evident in both the paretic and the nonparetic arms after stroke when forward reaching was resisted with viscous, elastic, or mass loads. The paretic arm responded with higher muscle activation and co-contraction levels across all load conditions than the matched control arm. Smaller increases in muscle activation and co-contraction levels that varied with load type were observed in the nonparetic arm. On the basis of the response of the nonparetic arm, this study provides preliminary evidence suggesting that viscous loads elicited strong muscle activation with minimal co-contraction. Further intervention studies are needed to determine whether viscous loads are preferable for poststroke resistive exercise programs.

Reliability of maximal static strength measurements of the arms in subjects with hemiparesis

OBJECTIVE

To evaluate the reliability of maximal static strength measurements of five arm muscle groups and of strength ratios (paretic/non-paretic) in subjects with poststroke hemiparesis.

DESIGN

The generalizability theory was used to estimate the reliability coefficients and standard errors of measurement of maximal strength for various combinations of trials and sessions and of the strength ratios for one and two sessions. Grip maximal voluntary force and/or maximal voluntary torques exerted by flexor and extensor muscles at both the elbow and shoulder joints were measured in 17 subjects with poststroke hemiparesis. Multiple trials were performed by subjects during two sessions.

SETTING

Rehabilitation centre.

SUBJECTS

A convenience sample of 17 subjects with poststroke hemiparesis.

RESULTS

The reliability coefficients for the strength measurements were in the range of 0.81-0.97 with standard errors of measurement accounting for 4% to 20% of the group means. For the strength ratios, the coefficients of generalizability ranged from 0.76 to 0.95 with standard errors of measurement equal to 6% to 19% of the group means.

CONCLUSIONS

The maximal strength measurements of the arms in subjects with hemiparesis are reliable. The strength ratios are also reliable and can be used to quantify strength impairment.