Analysis of the musculoskeletal loading of the thumb during pipetting--a pilot study.

Previous epidemiological studies indicate that the use of thumb-push mechanical pipettes is associated with musculoskeletal disorders (MSDs) in the hand. The goal of the current study was to analyze the loading in the muscle-tendon units in the thumb during pipetting. The hand is modeled as a multi-body linkage system and includes four fingers (index, long, ring, and little finger), a thumb, and a palm segment. Since the current study is focused on the thumb, the model includes only nine muscles attached to the thumb via tendons. The time-histories of joint angles and push force at the pipette plunger during pipetting were determined experimentally and used as model input; whereas forces in the muscle-tendon units in the thumb were calculated via an inverse dynamic approach combined with an optimization procedure. Results indicate that all nine muscles have force outputs during pipetting, and the maximal force was in the abductor pollicis brevis (APB). The ratio of the mean peak muscle force to the mean peak push force during the dispensing cycle was approximately 2.3, which is comparable to values observed in grasping tasks in the literature. The analysis method and results in the current study provide a mechanistic understanding of MSD risk factors associated with pipetting, and may be useful in guiding ergonomic designs for manual pipettes.

The musculoskeletal loading profile of the thumb during pipetting based on tendon displacement.

Strong evidence indicates that highly repetitive manual work is associated with the development of upper extremity musculoskeletal disorders (MSDs). One of the occupational activities that involves highly repetitive and forceful hand work is manual pipetting in chemical or biological laboratories. In the current study, we quantified tendon displacement as a parameter to assess the cumulative loading exposure of the musculoskeletal system in the thumb during pipetting. The maximal tendon displacement was found in the flexor pollicis longus (FPL) tendon. Assuming that subjects' pipetting rates were maintained constant during a period of 1 h, the average accumulated tendon displacement in the FPL reached 29 m, which is in the lower range of those observed in other occupational activities, such as typing and nail gun operations. Our results showed that tendon displacement data contain relatively small standard deviations, despite high variances in thumb kinematics, suggesting that the tendon displacements may be useful in evaluating the musculoskeletal loading profile.

Arch height index normative values of college-aged women using the arch height index measurement system.

BACKGROUND: The arch height index measurement system (AHIMS) device has been found to be a reliable and valid instrument for measuring the arch height index (AHI) of the feet of individuals; however, normative data for the AHI are lacking for various populations. Therefore, the purposes of this study were to establish population normative AHI values for college-aged females and to compare the observed AHI data across right and left feet. METHODS: Seventy-nine college-aged females served as study participants, and both feet were measured using the AHIMS in the seated and standing positions. The AHI was calculated as the ratio of the dorsum height of the foot at half the total foot length to the length of the foot from the heel to the base of the first metatarsophalangeal joint. RESULTS: The mean ± SD AHI values for the left and right feet in the seated position were 0.355 ± 0.031 and 0.369 ± 0.034, respectively. The mean ± SD AHI values for the left and right feet in the standing position were 0.338 ± 0.031 and 0.343 ± 0.033, respectively. There were significant differences observed between the left and right feet for the seated (P < .001) and standing (P = .003) positions. CONCLUSIONS: Normative values were established for college-aged females for the AHI using the AHIMS. Differences were noted between the right and left feet of the participants sampled. Although normative values were obtained, we caution against using these values to classify foot arch types based solely on a sample of the population studied.

Footwear and locomotor skill performance in preschoolers.

The effect of footwear on locomotor skill performance was examined. 12 children (4 boys, 8 girls; M age = 56.3 mo., SD = 3.3) served as participants. Participants were randomly assigned to perform the locomotor subscale of Ulrich's Test of Gross Motor Development in two shoe conditions (Condition 1: Stride Rite athletic shoes, and Condition 2: flip flop sandals). Children scored significantly higher when wearing athletic shoes than flip-flop sandals. This finding is relevant for motor performance and safety in physical education and movement programs.

Comparative analysis of human gait while wearing thong-style flip-flops versus sneakers.

BACKGROUND: Flip-flops are becoming a common footwear option. Casual observation has indicated that individuals wear flip-flops beyond their structural limit and have a different gait while wearing flip-flops versus shoes. This alteration in gait may cause the anecdotal foot and lower-limb discomfort associated with wearing flip-flops. METHODS: To investigate the effect of sneakers versus thong-style flip-flops on gait kinematics and kinetics, 56 individuals (37 women and 19 men) were randomly assigned to a footwear order (flip-flops or sneakers first) and were asked to wear the assigned footwear on the day before and the day of testing. On each testing day, participants were videotaped as they walked at a self-selected pace across a force platform. A 2 (sex) x 2 (footwear) repeated-measures analysis of variance (P = .05) was used for statistical analysis. RESULTS: Significant interaction effects of footwear and sex were found for maximal anterior force, attack angle, and ankle angle during the swing phase. Footwear significantly affected stride length, ankle angle at the beginning of double support and during the swing phase, maximal braking impulse, and stance time. Flip-flops resulted in a shorter stride, a larger ankle angle at the beginning of double support and during the swing phase, a smaller braking impulse, and a shorter stance time compared with sneakers. CONCLUSIONS: The effects of footwear on gait kinetics and kinematics is extensive, but there is limited research on the effect of thong-style flip-flops on gait. These results suggest that flip-flops have an effect on several kinetic and kinematic variables compared with sneakers.