Effect of an on-hip load-carrying belt on physiological and perceptual responses during bimanual anterior load carriage

Manual load carriage continues to be a major contributor of musculoskeletal injury. This study investigates the physiological and subjective effects of an on-hip load-carrying belt (HLCB) during bimanual anterior load carriage. Fifteen healthy male participants walked on a level ground treadmill at 4.5 km/h for 5 min carrying 5, 10 and 15 kg loads with hands and arms in front of the body, with and without using the HLCB (WD and ND). Heart rate, normalized oxygen uptake, minute ventilation and, central and peripheral ratings of perceived exertion were the dependent variables. The mean heart rate, normalized oxygen uptake, minute ventilation and peripheral rating of perceived exertion increased significantly with load under both WD and ND conditions. At a load of 15 kg, the mean heart rate, normalized oxygen uptake, minute ventilation and peripheral rating of perceived exertion were significantly lower by 6.6%, 8.0%, 11.8% and 13.9% respectively in WD condition when compared to the ND condition. There was no significant difference between WD and ND conditions with 5 or 10 kg load. It can be concluded that the HLCB could reduce a person's physiological and peripheral perceptual responses when walking on a level ground treadmill at 4.5 km/h with a load of 15 kg. Using a HLCB or similar device is therefore recommended for bimanual anterior load carriage for loads of 15 kg or probably larger.

Simplified subjective workload assessment technique

Although the subjective workload assessment technique (SWAT) has been widely used, it has two main problems: it is not very sensitive for low mental workloads and it requires a time-consuming card sorting pretask procedure. In this study are presented five variations of SWAT in an effort to overcome the limitations. Four of the variants used the continuous SWAT subscales while one used the discrete SWAT subscale. Fifteen subjects participated in the experiment. The scales were compared with the original SWAT scale in terms of sensitivity and pretask procedure completion time when performing arithmetic tasks. The results show that all four variants are more sensitive than the conventional SWAT scale and that the pairwise comparison procedure takes significantly less pretask completion time compared with the original SWAT scale. Thus, the conventional pretask procedure can be replaced by a simple unweighted averaging to yield a scale of high sensitivity.

Foot flare and foot axis

Most commercial footwear is designed and manufactured on a curved last, although the amount of curvature of the last and the turning point of the last centerline have not been formally determined. In this study, we used principal component analysis to determine the foot axis so that lasts that match feet can be produced, resulting in a good fit. In evaluating 50 Hong Kong Chinese participants, we found that the center of the foot is located at approximately 52% of the foot length measuring from the back of the foot (SD = 0.65%) and that Hong Kong participants have a mean inflare (inward curvature) of 3.2 degrees. The foot center and inflare measures will help determine the fit between footwear and feet. Applications of this research include the ability to incorporate foot flare into the design and manufacture of footwear.

Legality of bowling actions in cricket

An ergonomic methodology has been designed and developed to evaluate the legality of bowling actions in cricket. This paper describes the methodology and a case study related to an international cricket player with an unorthodox bowling action. Objective measurements were used to evaluate the action. An electrogoniometer and a force-sensing resistor (FSR) were used for this purpose. The electrogoniometer measured the elbow angles in the sagittal plane, while the FSR indicated the instant of ball release to assess the presence of any elbow 'straightening' directly preceding delivery. The FSR was attached to a finger depending on the type of ball delivered. Angles and forces were sampled at 500 Hz and stored in a data logger. The information collected was downloaded on to a computer for further analyses. The angle information preceding ball release is a clear indicator of arm 'straightening' during bowling. The methodology has high reliability and accuracy in the evaluation of the legitimacy of bowling actions as defined by the International Cricket Council laws.

Target-directed head movements in a head-coupled virtual environment: predicting the effects of lags using Fitts' law

Two experiments have investigated the effects of lag on discrete target-directed head movements in a virtual environment. Both the target and a head-slaved pointer (subjected to lag) were presented on a head-mounted display. Target-directed head movements in the presence of a constant time lag were shown to obey Fitts' law (R2 > .93). A previously reported interaction between the effects of lag and the effects of index-of-difficulty on hand movement time could not be found in head movement time when the target width was kept constant. Further experiments suggested that there is a significant interaction between the effects of target width and lag but not between target distance and lag. A model predicting head movement strategy in the presence of lag is proposed to explain the experimental findings. This model predicts, and experiments verified, that for a target width from 1 degree to 8 degrees and a target distance range of 2.5 degrees to 30 degrees, the effect of lag (up to 267 ms) on target-directed head movement is independent of target distance but dependent on target width. Actual or potential applications of this research include the design of virtual control panel and its layout in a Virtual Reality simulator.