This study investigated temporal changes in movement strategy and performance during fatiguing short-cycle work. Eighteen participants performed six 7-min work blocks with repetitive reaching movements at 0.5 Hz, each followed by a 5.5-min rest break for a total duration of 1 h. Electromyography (EMG) was collected continuously from the upper trapezius muscle, the temporal movement strategy and timing errors were obtained on a cycle-to-cycle basis, and perceived fatigue was rated before and after each work block. Clear signs of fatigue according to subjective ratings and EMG manifestations developed within each work block, as well as during the entire hour. For most participants, timing errors gradually increased, as did the waiting time at the near target. Changes in temporal movement strategy were negatively correlated with changes in the level and variability of EMG, suggesting that an adaptive temporal strategy offset the development of unstable motor solutions in this fatiguing, short-cycle work.Practitioner Summary: Sustained performance of operators is essential to maintain competitiveness. In this study of repetitive work, participants gradually changed their temporal movement strategy, for possibly alleviating the effects of fatigue. This suggests that in order to effectively counteract fatigue and sustain performance, industrial production should allow extensive spatial and temporal flexibility.
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Background: Development of more effective interventions for nonspecific chronic low back pain (LBP), requires a robust theoretical framework regarding mechanisms underlying the persistence of LBP. Altered movement patterns, possibly driven by pain-related cognitions, are assumed to drive pain persistence, but cogent evidence is missing. Aim: To assess variability and stability of lumbar movement patterns, during repetitive seated reaching, in people with and without LBP, and to investigate whether these movement characteristics are associated with painrelated cognitions. Methods: 60 participants were recruited, matched by age and sex (30 back-healthy and 30 with LBP). Mean age was 32.1 years (SD13.4). Mean Oswestry Disability Index-score in LBP-group was 15.7 (SD12.7). Pain-related cognitions were assessed by the ‘Pain Catastrophizing Scale’ (PCS), ‘Pain Anxiety Symptoms Scale’ (PASS) and the task-specific ‘Expected Back Strain’ scale(EBS). Participants performed a seated repetitive reaching movement (45 times), at self-selected speed. Lumbar movement patterns were assessed by an optical motion capture system recording positions of cluster markers, located on the spinous processes of S1 and T8. Movement patterns were characterized by the spatial variability (meanSD) of the lumbar Euler angles: flexion-extension, lateralbending, axial-rotation, temporal variability (CyclSD) and local dynamic stability (LDE). Differences in movement patterns, between people with and without LBP and with high and low levels of pain-related cognitions, were assessed with factorial MANOVA. Results: We found no main effect of LBP on variability and stability, but there was a significant interaction effect of group and EBS. In the LBP-group, participants with high levels of EBS, showed increased MeanSDlateral-bending (p = 0.004, η2 = 0.14), indicating a large effect. MeanSDaxial-rotation approached significance (p = 0.06). Significance: In people with LBP, spatial variability was predicted by the task-specific EBS, but not by the general measures of pain-related cognitions. These results suggest that a high level of EBS is a driver of increased spatial variability, in participants with LBP.
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This dissertation describes the dynamics of motor competence (MC) development from early childhood (EC) to middle childhood (MCD). Being motor competent in early childhood creates a window of opportunity for taking part in physical activities later in childhood and adulthood. However, there is a worrying trend in MC development during childhood. This trend shows that, last decades, children struggle more with executing fundamental movement skills (e.g., hopping, dribbling, balancing, throwing and catching) and that general motor fitness levels of children are decreasing. A delay in MC development during childhood has a negative impact on the general health status later in life. Therefore, it is important to support young children to develop their MC. The main research question of this dissertation was: How can motor competence be promoted as efficient and effective as possible in early childhood by sport professionals? Chapter 2 showed that MC development from early to middle childhood proceeds with variation. The majority of the children had a stable ‘normal’ or increasing ‘high’ development of MC over time. However, a concerning level of 18.2% of the young children showed an undesirable pattern (i.e., a negative course of motor development over time and a ‘low’ MQ score during the final measurement) of MC development as they grow older. Chapters 3 and 4 showed that characteristics of the social and physical home environment and direct living environment were associated with MC disparities during early childhood. Both parenting practices and parental PA-involved behaviours were relevant modifiable factors. For example, stronger parental active transportation routines and PA parental practices decreased the odds of a lower MC. Also, the presence of a home garden decreased the likelihood of children being classified as low motor competent. With regard to gender differences, girls showed lower levels of MC compared to boys. Special attention should also be paid to obese children as they experience less enjoyment of PA compared with normal weighted peers (chapter 3). Excessive body weight is also a risk factor associated with an undesirable MC development, just like lack of sports participation (chapter 5). Intervention strategies (chapter 6) incorporating all fundamental movement skills with a great variety of activities for at least 3 to 4 times a week seem to be most effective to stimulate MC development. Methodological and didactical aspects like deliberate practice and play should be implemented together with training and coaching sessions for sport professionals to increase the effectiveness of the interventions. With respect to the efficiency of promoting MC development, policy makers and sport professionals should pay more attention on early childhood and especially focus on those children at risk for a delay in MC development. So, overweighted children and children not participating in organized sports should be given more attention by sport professionals. Additionally, the effectiveness of MC interventions can be increased by making use of the home environment, childcare context and school context of young children. Sport professionals can act as connectors between parents, school, and sports clubs.
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