THE EFFECTS OF DIFFERENT TRUNK INCLINATIONS ON BILATERAL TRUNK MUSCULAR ACTIVITIES, CENTRE OF PRESSURE AND FORCE EXERTIONS IN STATIC PUSHING POSTURES.

In order to reconcile contradictory results from previous studies on manual pushing, a study was conducted to examine the effect of trunk inclination on muscular activities, centre of pressure (COP) and force exertion during static pushing. Ten subjects pushed at 0 degrees, 15 degrees, 30 degrees, and 45 degrees body inclinations in parallel and staggered feet stances. Wall and ground force plates measured pushing force, wall COP, vertical ground reaction force (GRF) and ground COP. Electromyogram data were recorded at 10 trunk muscle sites. Pushing force was found to increase with body inclination. GRF peaked at 15 degrees and reached its lowest level at the 45 degrees inclination. The lowest wall force plate standard deviation of COP displacement was found at the 30 degrees inclination. The lowest low back muscular activity was found at the 15 degrees and 30 degrees inclinations. Based on force exertion, muscular load, and stability, the 30 degrees body inclination was found to be the best posture for static pushing. This study also showed asymmetry in muscular activity and force exertion which has been received less attention in manual pushing studies. These findings will require further study.

The relation between the changes of postural achievement, lower limb muscle activities, and balance stability in three different deep-squatting postures.

Deep squatting places a burden on the lower limb muscles and influences postural balance. We attempted to determine the effects of postural changes on the rectus femoris, tibialis anterior, gastrocnemius, soleus, and extensor digitorum brevis muscles during squatting in 8 healthy male subjects. Three squatting conditions were involved: full squatting (FS), tiptoe squatting (TT), and tiptoe squatting on a 15 degrees slope (TTS), performed randomly and recorded in a period of 4 min for each task. The influence of the squatting condition on electromyography and vertical ground reaction force parameters was examined in order to observe the effect of postural alteration on muscle activity and balance control. The results showed that the change of squatting posture from FS to TT decreased the activity of the rectus femoris and tibialis anterior muscles. FS has been suspected as a main cause of musculoskeletal complaint during prolonged squatting. In contrast, as the heel was lifted, the extensor digitorum brevis muscle increased to 39% of maximum activation. On the other hand, sway analysis at TT showed balance instability regarding the large area occupation of the center of pressure displacement. The presence of a 15 degrees slope significantly reduced the muscular load. This simple study suggests that the inclusion of a sloping surface in daily activities that requires a squatting posture would be an effective means to reduce muscular load.

The influence of different lower seat height on the muscular stress during squatting for a ground level job.

Work requiring extremely body flexion is strongly associated with a high incidence of musculoskeletal injuries often reported during adopting squatting. In this study, the influence of different lower seat heights on the muscular stress in squatting on a stool (SS) were examined in comparison with fully squatting (FS). Fourteen healthy Indonesian males were recruited in the experiment. Two-dimensional body kinematics, ground reaction force (GRF) and electromyography (EMG) data were collected as subjects performed forward movement under four squatting height conditions which were FS and SS at 10 cm, 15 cm and 20 cm seat height. The results demonstrated that the change from FS to SS primarily affected the segmental angular flexions and muscular activities in the upper and lower limbs. GRF data showed that the SS conditions delivered 24% body weight onto the seat. The change of FS to SS showed significantly decrease in muscular load of the rectus femoris and tibialis anterior. In contrast, the soleus and gastrocnemius increased the activities as the seat height increased. The type of task that required the hand to handle the object on the ground level affected the trunk to be more flexed as the seat height increased. The findings of this study suggest that the use of a lower seat stool of a proper height seems to be a sub-optimal solution considering the change of muscular load associated with the discomfort in a squatting posture.

The evaluation of the effect of stool height alteration on workload of squatting postures performed by Indonesians with different body mass index (BMI).

Indonesians commonly perform activities on the floor that require squatting postures. It has been identified that adopting squatting postures without any proper support would gradually cause postural stress. This study examines the influence of different squatting heights to the body kinematics and subjective discomfort rating. The subjects were divided into two different body types: overweight subjects with BMI > 24.9 and normal weight subjects with BMI 18-24.9. The subjects adopted a squatting posture at no-stool condition and at the stool height of 10, 15, and 20 cm. The task was to simulate the work close to the ground level with the hip joint deeply flexed. Body segmental angular flexion (SAF) and the visual analog scale (VAS) method were selected for parameter analyses. Significant differences were found in both parameters SAF (trunk, hip, knee, and ankle) and VAS. The interaction effect was found by squatting height and the body type for SAF of the trunk (p < 0.05). However, the increasing BMI index was also found significantly affected associated with the anthropometrical characteristics for buttock height and lower limbs depth. It is suggested that normal weight subjects sit comfortably at 15 cm stool height, whereas overweight subjects preferred 20 cm stool height as a better acceptability condition in terms of overall parameter analyses.