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Design of Manual Handling and Load Carriage Tasks
Published in R. S. Bridger, Introduction to Human Factors and Ergonomics, 2017
Rucksack palsy is an injury that can be caused by carrying rucksacks. Excess pressure on the neck can damage the nerve roots at C5 and C6 causing numbness and pain. Sometimes, the serratus anterior muscle can be weakened, causing the appearance of a “winged” scapula. The serratus anterior muscle forms part of the scapula-thoracic joint which holds the scapula against the thorax. Rucksack palsy can be caused by badly fitting rucksacks and is less likely if the rucksack has a hip strap to enable the load to be transmitted directly to the pelvis, rather than via the shoulders.
Comparison of throwing kinematics and muscle activation of female elite handball players with and without pain – the effect of repeated maximal throws
Published in Sports Biomechanics, 2023
Tina Piil Torabi, Birgit Juul-Kristensen, Mogens Dam, Mette K Zebis, Roland van den Tillaar, Jesper Bencke
Furthermore, before maximal shoulder extension, the serratus anterior increased muscle peak activity after the FFP and after the maximal shoulder extension the muscle peak activity, decreased in both groups. Before the maximal shoulder extension, the serratus anterior contributes to upwardly rotate the scapula. The scapula provides a stable base to transfer forces from the trunk to the shoulder and arm during throwing, and to stabilise the shoulder joint, while creating space in the subacromial area by elevating the acromion when elevating the arm (DiGiovine et al., 1992; Meister, 2000; Mihata et al., 2015). Earlier studies (Kibler et al., 2013; Meister, 2000; Neer, 2005) have described muscle force couples for the scapula, which includes upper and lower parts of the trapezius paired with the serratus anterior muscle. To elevate the acromion, the muscle force couple of the lower trapezius and serratus must be appropriate. The analysis shows a significant interaction in the timing of the upper trapezius before maximal humeral extension, and an increased muscular activity in the serratus anterior after the FFP before the maximal shoulder extension, and this may be a compensation for the stable changes of muscle peak activity in the upper and lower trapezius, change in timing of the upper trapezius, and the increased maximal external shoulder rotation (Figure 6). A decreased elevation of the acromion will decrease the subacromial space and increase the risk of subacromial impingement (Meister, 2000; Neer, 2005). Earlier studies have described that forces generated during the overhead throwing motion create stress across the shoulder joint, and can develop damage in the joint, even though no earlier injury has been registered (Escamilla & Andrews, 2009; Escamilla et al., 2007, 2014; Jobe et al., 1989). Therefore, based on this analysis, the importance of a well-coordinated muscle recruitment of the scapula humeral muscles will impact the kinematics of the overhead throwing motion while playing with or without shoulder pain.
Skill level and forearm muscle fatigue effects on ball speed in tennis serve
Published in Sports Biomechanics, 2021
Lin-Hwa Wang, Kuo-Cheng Lo, Fong-Chin Su
According to Morris, Jobe, Perry, Pink, and Healy (1989), forearm position and power are supported by the active pronator during the acceleration phase. The extensor carpi radialis brevis (ECRB), extensor digitorum communis (EDC) and extensor carpi radialis longus (ECRL) muscles are extremely active at the wrist during the cocking phase, with activity increasing during the late-cocking phase (> 40% MMT) as the possible primary source of stability of the wrist joint when the racket is gripped during a tennis serve (Morris et al., 1989; Rota et al., 2014). During the cocking phase, the bicep brachii muscle activity increases during elbow flexion. The corresponding stabilisation of the shoulder and scapula is caused by supraspinatus muscle activity and serratus anterior muscle activity, respectively (Moynes, Perry, Antonelli, & Jobe, 1986). In the current study, all muscle activity differed between expert and non-expert groups during the cocking and acceleration phases of top-spin serve in non-fatigued and fatigued states. A significant increase in activity of the ECU and ECR for extension was observed. Both the ECU and ECR might be responsible for maintaining the stability of the wrist joint and the racket handle for the coming acceleration and impact in fatigue during tennis serving. Collaboration at the wrist joint consisted of flexor functions during racket gripping and an antagonistic effect from wrist extensor contractions. The differences regarding the ECR and ECU between expert and non-expert groups were significantly greater during fatigue. Muscle activity, especially for the ECR and ECU, declined as participants’ age increased (p = 0.001). In this study, muscle activity during fatigue was significantly higher than it was during non-fatigue, which might be attributed to a greater reliance on the wrist extensor during fatigue. This compensation strategy was described by Bonnard, Sirin, Oddsson, and Thorstensson (1994), who examined the knee extensor during hopping and revealed a trade-off between muscles at different joints. In the current study, the decline of muscle activity for the non-expert group was greater than that for the expert group. The loss of force-generating capacity, which resulted in the aforementioned compensation strategy, may be attributed to the influence of ageing. A low exercise-to-rest ratio in matches may help tennis players recover faster and delay the onset of fatigue. To maintain a certain performance level, different neuromuscular adjustments are employed by the central nervous system to overcome fatigue effects (Maquirriain et al., 2016).