The level of muscle activity can be decreased with optimized foot wedge condition. The aim of this study was to evaluate the effect of different foot wedge conditions on the activity of selected lower extremity muscles during load lifting. Nine able‐bodied male subjects participated in this study. Electromyography activity of the vastus medialis (VM), vastus lateralis (VL), medialis gastrocnemius (MG), and soleus (SOL) muscles was recorded during dynamic load lifting using the squat technique in 5 conditions: i) non‐wedge (NW), ii) 1 cm heel height increasing (PW1), iii) 3 cm heel height increasing (PW3), iv) 1 cm in front of the feet (AW1), and v) 1 cm inside the feet (MW1). The results showed that the VM activity decreases in the MW1 compared to other conditions and significantly compared to the PW1 and PW3 conditions (p < .05). Decreases in the VL activity in the AW1 as well as in descending and ascending phases of MW1 were observed (p < .05). Also in the descending phase, the SOL activity in AW1 decreased significantly compared to NW condition (p < .05). However, there was no significant difference in MG activity between different conditions (p > .05). It seems that placing wedges in the anterior and medial area of the feet may decrease quadriceps muscles activity and probably can delay reaching time to fatigue during load lifting. These findings may be helpful in designing special shoes for ergonomics fields and work environments. 相似文献
This study aimed at investigating the effects of a novel neck balance system (NBS), which is a baseball cap with counterweights in the occipital part, on neuromuscular fatigue of neck muscles during and after a full‐range repeated neck flexion‐extension task. Surface electromyography (sEMG) of sternocleidomastoid (SCM) and semispinalis capitis (SC) muscles was recorded in 15 healthy individuals during full‐range flexion‐extension movements of the neck lasting 5 min at a fixed pace (1 Hz), with or without NBS. Maximal isometric force and sEMG were recorded before and after the fatiguing task. During the fatiguing task, the SC muscle showed a higher decline in amplitude of sEMG with NBS than without NBS, while no differences in the SCM muscle emerged between the two conditions. Maximal isometric force of both neck flexor and extensor muscles decreased significantly after the fatiguing task, both with NBS (p < .05) and without NBS (p < .05), with no differences between the two conditions. In conclusion, adopting the NBS promotes an increase of the activation of neck extensor muscles, possibly leading to earlier decline of the neuromuscular performance and to diminished ability to actively stabilize neck structures. For these reasons, the adoption of the NBS during dynamic, fatiguing contractions may not be appropriate. 相似文献
Tablets are much heavier than smartphones and able to bring more musculoskeletal disorders in the upper extremities. The aim of this study was to understand the effects of tablet location on the recruitment of muscles in the neck and upper extremities. Fifteen healthy volunteers typed the lyrics while listening to a song at three tablet locations for 5 min. An iPad 2 was randomly located at one of the levels with 70, 90, and 130 degrees of elbow flexion in sitting. Typing duration, frequency of typing error, perceived levels of fatigue, and subjective position preferences were recorded and recruitment of muscles in the neck and upper extremities was measured. Muscle recruitment of three parts of the trapezius and biceps brachii decreased and use of the levator scapula increased as the vertical level of the tablet heightened. Self‐reported discomfort increased significantly in the neck, upper back, shoulders, elbows, and wrists over time regardless of the tablet location. The table location affected the self‐reported discomfort only at the elbow joints. Subjective preference was highest at the lowest tablet location with the 130‐degree elbow flexion. The vertical levels of the tablet and typing duration independently affected the muscle recruitment and self‐reported discomfort. Findings of this study can be helpful for tablet users in preventing musculoskeletal disorders in the upper extremities. 相似文献
Patterns of cervical muscle activity may contribute to overuse injuries in office workers. The purpose of this investigation was to characterise patterns of upper trapezius muscle activity in pain-free office workers using traditional occupational exposure measures and a modified Active Amplitude Probability Distribution Function (APDF), which considers only periods of active muscle contraction. Bilateral trapezius muscle activity was recorded in 77 pain-free office workers for 1–2 full days in their natural work environment. Mean amplitude, gap frequency, muscular rest and Traditional and Active APDF amplitudes were calculated. All measures demonstrated fair to substantial reliability. Dominant muscles demonstrated higher amplitudes of activity and less muscular rest compared to non-dominant, and women demonstrated less muscular rest with no significant difference in amplitude assessed by Active APDF compared to men. These findings provide normative data to identify atypical motor patterns that may contribute to persistence or recurrence of neck pain in office workers.
Practitioner Summary: Upper trapezius muscle activity was characterised in a large cohort of pain-free workers using electromyographic recordings from office environments. Dominant muscles demonstrated higher activity and less rest than non-dominant, and women demonstrated less rest than men. Results may be used to identify atypical trapezius muscle activity in office workers. 相似文献
The performance of manual material handling tasks is one major cause of lower back injuries. In the current study, we investigated the influence of the weight configuration of hand loads on trunk muscle activities and the associated spinal stability. Thirteen volunteers each performed static weight-holding tasks using two different 9 kg weight bars (with medial and lateral weight configurations) at two levels of height (low and high) and one fixed horizontal distance (which resulted in constant spinal joint moment across conditions). Results of the current study demonstrated that holding the laterally distributed load significantly reduced activation levels of lumbar and abdominal muscles by 9–13% as compared with holding the medially distributed load. We believe such an effect is due to an elevated rotational moment of inertia when the weight of the load is laterally distributed. These findings suggest that during the design and assessment of manual material handling tasks, such as lifting and carrying, the weight configuration of the hand load should be considered.
Practitioner summary: Elevated trunk muscle activities were found when holding a medially distributed load vs. a laterally distributed load (with an equivalent external moment to the spine), indicating a reduced spinal stability due to the reduced rotational moment of inertia. The configuration of the hand load should be considered when evaluating manual material handling tasks. 相似文献
The sEMG signals are collected from the vastus lateralis,vastus medialis,biceps femoris,and semitendinosus of lower extremity during level walking among control subjects and knee osteoarthritis (OA) pa... 相似文献