Analysis of self-reported problematic tasks for pregnant women.

The objective of this study was to identify major components of, and influential factors in, problematic tasks performed by pregnant women employed in education, health care and service areas. Seventy-two pregnant women were surveyed using specially designed questionnaires consisting of an Initial Survey, a Job Analysis Questionnaire and a Task Description Questionnaire. Forty-four subjects (60%) had difficulty performing at least one work task and reported 105 tasks that were problematic at work. Reaching above the head, bending forward, bending and twisting, pushing, repeating actions and working at a fast pace were identified as the task components requiring the greatest level of effort. Excessive effort, excessive time, getting tired, repetitive actions, stress and fear of injury were identified as factors that had strong associations with the six major task components. Findings of this study suggest that these task components and factors should be considered when designing, assigning or analysing tasks for working pregnant women.

Prediction of back strength using anthropometric and strength measurements in healthy females.

OBJECTIVES: The purpose of this study was to develop a regression equation to predict back extensor maximal voluntary contraction (back strength) for females based on several anthropometric and strength measurements using a multiple regression technique. BACKGROUND: Back strength is an important parameter in low back pain studies. However, the measurement of back strength is problematic in certain populations such as low back pain patients and pregnant women. METHODS: Back strength was measured as both moment at L4/L5 and force. Ten anthropometric or strength measurements were chosen to develop the prediction equation. The data used for developing the models were from eighty non-pregnant female subjects, age 18-42 and with no history of back pain in the past year. Backwards stepwise analysis was performed in order to choose the best fit predictors. The predictive ability of each of the models was checked using the cross-validation technique on 20 other subjects. FINDINGS: Two prediction models were developed for moment and force, respectively. The models explained 46.9% and 48.2% of the variance in back strength. No multicollinearity problem was found. The validation study showed that the observed back strength was highly correlated with the predicted back strength. INTERPRETATION: Mass, height, trunk length, grip strength and quadriceps strength are the best predictors of back strength in this study. The models developed in this study can be used for both general female low back pain patients and the pregnancy population.

Muscle function at the wrist after eccentric exercise.

PURPOSE: The purpose of this experiment was to investigate the effects of eccentric exercise by the wrist extensor muscles on the function and motor control of synergist wrist extensor muscles and the antagonist wrist flexor muscles. METHODS: Ten subjects were tested repeatedly over a period of 11 d, once before and four times after a bout of strenuous eccentric exercise with the wrist extensor muscles. Tests performed as indicators of muscle injury were wrist extension MVC, ROM, and soreness. Tests performed as measures of function and motor control were maximum joint velocity, ability to sustain a constant torque, and the ability to track a changing torque. RESULTS: Indicators of muscle injury: subjects exhibited a decline in wrist extension MVC and ROM, which peaked on day 1, and reported that muscle soreness was greatest on day 2. All measures returned to baseline values by day 10. Measures of function and motor control: subjects exhibited a greater difficulty sustaining a submaximal contraction and tracking torque after eccentric exercise. Greater torque variances in these tests were most evident at high torque levels. Subjects exhibited the greatest difficulty 24 h after eccentric exercise and had recovered by day 10. There was no change in maximal wrist extension velocity. CONCLUSIONS: Strenuous eccentric exercise by wrist extensors had an effect on function and motor control of the wrist extensor muscles. The effect was most evident during contractions in which high torque was required. The response of all of the wrist extensors after the exercise bout was similar, suggesting that they operated in a synergistic manner. The antagonists wrist flexors showed increased coactivation after eccentric exercise.

Motor impairment in the human hand following eccentric exercise.

Motor impairment was induced by having subjects perform two sets of 50 maximal contractions, using the first dorsal interosseus (FDI) muscle to abduct the index finger, while the muscle was being stretched. Tests were conducted prior to the exercise (pre-exercise) and 24 h following the exercise (post-exercise). There were declines of 19% in maximal abduction torque and 15% in maximal flexion torque at the metacarpaphalangeal joint, during isometric contraction post-exercise compared to pre-exercise. The ability to stabilize the metacarpophalangeal joint about the abduction/adduction axis was reduced by 14% post-exercise, and the variability in tracking an isometric torque target increased by 30%. There was a decrement of 7%-10% in the median frequency of the power density spectrum of FDI electromyogram (EMG) throughout a 60 s maintained abduction at 50% maximal voluntary contraction. The mean rectified EMG, on the other hand, increased by 100%-175% for torque levels below 40% of maximal voluntary contraction, post-exercise. The results were consistent with preferential injury of type II muscle fibres in FDI. Although non-exercised synergist muscles appeared to be inhibited during maximal voluntary flexion, there was evidence that they compensated for injured FDI muscle fibres during maintained contraction at sub-maximal flexion torque.

Passive and active wrist joint stiffness following eccentric exercise.

The purpose of this study was to investigate the effects of exercise-induced muscle injury on passive and active wrist joint stiffness. Ten male subjects were repeatedly tested over a period of 11 days, once prior to, and four times following a bout of eccentric exercise with the wrist extensor muscles. Static wrist stiffness was measured by applying a 3 degrees ramp and hold displacement of the manipulandum, which stretched the wrist extensor muscles. Wrist extension maximum voluntary contraction (MVC) declined by 24.5% from pre-exercise to 24 h after the exercise bout (P < 0.001). There was a reduced passive range of motion (ROM) from 82.8 degrees pre-exercise to 70.2 degrees on day 1 (P < 0.01), but no change in the passive joint stiffness at the neutral joint position, suggesting mechanical changes in the non-contractile tissues, or swelling that only resisted movement at the extremes of the ROM. Active joint stiffness at 50% pre-exercise MVC declined from 0.299 Nm deg(-1) pre-exercise to 0.254 Nm deg(-1) on day 1 (P < 0.025). Active joint stiffness at 10% pre-exercise MVC did not change on any of the days of testing compared to pre-exercise. These findings may indicate that large muscle fibers were more affected by the injury than small muscle fibers.

The effect of eccentric exercise on intrinsic and reflex stiffness in the human hand.

OBJECTIVE: The purpose of this work was to determine the effect of strenuous eccentric exercise on joint stiffness and to separate joint stiffness into components due to intrinsic muscle mechanics and delayed reflex muscle activation. DESIGN: Subjects performed 100 maximal eccentric contractions, using the first dorsal interosseus muscle to abduct the index finger while undergoing a 20 degrees displacement of the metacarpophalangeal joint. Joint stiffness was measured 24 h later during 15% and 65% maximal voluntary contraction and during electrical muscle stimulation at 15% of maximal voluntary contraction torque. BACKGROUND: Joint stiffness can be varied by changing voluntary muscle activation and thereby serves an important role in joint stabilization. Eccentric exercise has been shown to result in muscle fiber injury, reducing maximal muscle force. However, it is not known whether intrinsic muscle stiffness or reflex stiffness is also affected. METHODS: Displacements of 3 degrees amplitude were used to estimate joint stiffness about the neutral angle of the index finger. The difference between measurements made during voluntary muscle activation and electrical muscle stimulation was used to obtain reflex stiffness. RESULTS: There was no change in the passive joint stiffness nor was there any change in either the intrinsic or reflex stiffness at 15% maximal voluntary contraction. However, intrinsic stiffness for the electrically stimulated muscle was higher post-exercise than pre-exercise, while active joint stiffness at 65% maximal voluntary contraction (comprising intrinsic and reflex stiffness) was lower. CONCLUSION: The observed mechanical changes are compatible with the hypothesis that type II muscle fibers are more susceptible to injury than type I muscle fibers, which have higher intrinsic stiffness. RELEVANCE: Muscle stiffness is important for maintaining mechanical stability of a joint. The effects of eccentric exercise on muscle stiffness are likely analogous to the effects of muscle injury, making this a good model for biomechanical changes associated with muscle injury.

Inability to activate muscles maximally during cocontraction and the effect on joint stiffness.

In order to determine the maximum joint stiffness that could be produced by cocontraction of wrist flexor and extensor muscles, experiments were conducted in which healthy human subjects stabilized a wrist manipulandum that was made mechanically unstable by using positive position feedback to create a load with the characteristics of a negative spring. To determine a subject's limit of stability, the negative stiffness of the manipulandum was increased by increments until the subject could no longer reliably stabilize the manipulandum in a 1 degree target window. Static wrist stiffness was measured by applying a 3 degree rampand-hold displacement of the manipulandum, which stretched the wrist flexor muscles. As the load stiffness was made more and more negative, subjects responded by increasing the level of cocontraction of flexor and extensor muscles to increase the stiffness of the wrist. The stiffness measured at a subject's limit of stability was taken as the maximum stiffness that the subject could achieve by cocontraction of wrist flexor and extensor muscles. In almost all cases, this value was as large or larger than that measured when the subject was asked to cocontract maximally to stiffen the wrist in the absence of any load. Static wrist stiffness was also measured when subjects reciprocally activated flexor or extensor muscles to hold the manipulandum in the target window against a load generated by a stretched spring. We found a strong linear correlation between wrist stiffness and flexor torque over the range of torques used in this study (20-80% maximal voluntary contraction). The maximum stiffness achieved by cocontraction of wrist flexor and extensor muscles was less than 50% of the maximum value predicted from the joint stiffness measured during matched reciprocal activation of flexor and extensor muscles. EMG recorded from either wrist flexor or extensor muscles during maximal cocontraction confirmed that this reduced stiffness was due to lower levels of activation during cocontraction of flexor and extensor muscles than during reciprocal contraction.