The study by Barbusse et al. (2024) investigated how motor control of arm movements is affected by reversed gravity. It is commonly assumed that the central nervous system contains an internal gravity model, and that this model is used to optimize movements to minimize effort under the influence of gravity (e.g., Berret et al., 2008). Previously, the effect of decreased and increased gravity was investigated, and it was shown that people were able to adapt to this novel environment in a matter of minutes or days (e.g., Gaveau et al., 2011). Therefore, the authors investigated the effect of inverse gravity on motor control of arm movements.

In this study, an experiment was performed in which participants were placed in an inversion table and asked to perform as many pointing movements with their shoulder as possible in 12 blocks. In each block, the inversion table was placed either in the head-up or head-down position, and the position was switched every 35 seconds, starting from the head-up position. After 4 blocks, a 90 second break was taken. It was found that movement duration and amplitude did not significantly differ between both orientations. An analysis of the difference in time to peak acceleration, time to peak velocity, and time to peak deceleration between upward and downward movements revealed no significant difference for the peak acceleration, while for the peak velocity, the time difference was significantly smaller in the head-down than the head-up position, and for the peak deceleration, the time difference changed in the head-down position with the number of blocks, reaching a value more similar to the head-up (baseline) position.

The time to peak acceleration did not reverse for the head-down position, which showed that the central nervous system is not able to take advantage of gravity when it is placed in a head-down position, since it does not take advantage of the “free” acceleration provided by gravity. A longer exposure to inverse gravity might allow the body to adapt and re-optimize its internal gravity model to the new situation. The time difference was significantly different for the deceleration, but not for acceleration, which indicates that the movement was adapted mainly by feedback control, but that feedforward control remained largely the same. This further supports the conclusion that the central nervous system had not yet adapted its internal gravity model, and that re-optimization starts with adapting feedback control (Izawa et al., 2008). An important limitation is the discomfort that is experienced in the head-down position, which not only changes gravity, but also created negative physiological responses.

References

Denis Barbusse, Sarah Amoura, Jérémie Gaveau, Olivier White (2024) Feedback-driven adaptation of gravity-related sensorimotor control to an upside-down posture. OSF preprints, ver.3 peer-reviewed and recommended by PCI Health & Movement Sciences. https://doi.org/10.17605/OSF.IO/D9JPF.

Berret B, Darlot C, Jean F, Pozzo T, Papaxanthis C, Gauthier JP (2008) The inactivation principle: mathematical solutions minimizing the absolute work and biological implications for the planning of arm movements. PLoS computational biology, 4, e1000194. https://doi.org/10.1371/journal.pcbi.1000194

Gaveau J, Paizis C, Berret B, Pozzo T, Papaxanthis C (2011) Sensorimotor adaptation of point-to-point arm movements after spaceflight: the role of internal representation of gravity force in trajectory planning. Journal of Neurophysiology, 106, 620–629. https://doi.org/10.1152/jn.00081.2011

Izawa J, Rane T, Donchin O, Shadmehr R (2008) Motor adaptation as a process of reoptimization. The Journal of Neuroscience: The Official Journal of the Society for Neuroscience, 28, 2883–2891. https://doi.org/10.1523/JNEUROSCI.5359-07.2008

This study by Mathieu et al. (2024) builds on previous computational research showing that human arm movements use gravity to save energy and be more efficient (Berret et al., 2008; Crevecoeur et al., 2009; Gaveau et al., 2014, 2021), as well as on experimental research showing that kinematic and electromyographic markers are directly related to this energetic efficiency (Gaveau et al., 2016). 
 
The primary objective of this study by Mathieu et al. (2024) was to compare the effect of age on movement efficiency in an upper limb task and three whole-body tasks. These two types of tasks are often studied independently in the literature. Therefore, testing them in the same study allows the generalizability of the effect of age on movement efficiency to be examined. Electromyographic and kinematic patterns were compared in younger (n = 20) and older adults (n = 24), and movement efficiency was assessed using an index based on the activity of antigravity muscles. Results suggest that the effect of age is dependent on the type of movement. Specifically, older adults used gravity less than younger adults when performing whole-body movements, whereas no such age effect was evidenced when performing arm movements. The authors interpret this effect as an adaptation of whole-body movement strategies that compensates for age-related changes in body structures and functions to stabilize postural balance.
 
These findings contribute to the literature on postural control and how it differs from movement control that does not include the constraint of maintaining body balance, i.e., avoiding falls. Specifically, these results suggest that our brain implements a movement strategy specific to movements that require body balance, and that the efficiency of this strategy is affected by age. Further research would help to determine whether this efficiency, although altered, remains optimal throughout the age-related decline of body systems, or whether priorities change across aging, with stability and fall avoidance becoming more valued than energetic efficiency.​
 
References
- Berret, B., Darlot, C., Jean, F., Pozzo, T., Papaxanthis, C., & Gauthier, J. P. (2008). The inactivation principle: mathematical solutions minimizing the absolute work and biological implications for the planning of arm movements. PLoS Computational Biology, 4(10), e1000194. https://doi.org/10.1371/journal.pcbi.1000194
- Crevecoeur, F., Thonnard, J. L., & Lefèvre, P. (2009). Optimal integration of gravity in trajectory planning of vertical pointing movements. Journal of Neurophysiology, 102(2), 786–796. https://doi.org/10.1152/jn.00113.2009
- Gaveau, J., Berret, B., Angelaki, D. E., & Papaxanthis, C. (2016). Direction-dependent arm kinematics reveal optimal integration of gravity cues. eLife, 5, e16394. https://doi.org/10.7554/eLife.16394
- Gaveau, J., Grospretre, S., Berret, B., Angelaki, D. E., & Papaxanthis, C. (2021). A cross-species neural integration of gravity for motor optimization. Science Advances, 7(15), eabf7800. https://doi.org/10.1126/sciadv.abf7800
- Mathieu, R., Chambellant, F., Thomas, E., Papaxanthis, C., Hilt, P., Manckoundia, P., Mourey, F., & Gaveau J. (20024). Comparing arm to whole-body motor control disambiguates age-related deterioration from compensation. bioRxiv, version 5. Peer-reviewed and recommended by Peer Community in Health and Movement Sciences. https://doi.org/10.1101/2024.02.16.576683

This article (Goubran et al., 2024) presents a comprehensive systematic review and meta-analysis examining the relationship between kinesiophobia and physical activity. The inclusion of multiple health conditions and diverse measures of physical activity and kinesiophobia provides a broad perspective on the issue. 

Kinesiophobia (i.e., an excessive, irrational, and debilitating fear of movement) is thought to contribute to negative affective associations towards physical activity and avoidance behaviors, leading to decreased engagement in physical activity. Thus, the relationship between kinesiophobia and physical activity merits further investigation, particularly in health conditions where physical activity has a preventative and/or therapeutic role. 

The results of this meta-analysis (k = 83, n = 12,278) indicate a small-to-moderate negative correlation between kinesiophobia and physical activity (r = −0.19; 95% CI: −0.26 to −0.13; I2 = 85.5%; p < 0.0001.) Substantial heterogeneity and publication bias were noted, but p-curve analysis suggested true effects. Notably, this finding was consistent across studies using both self-report and objective device-based measures, and there was no evidence of a moderating effect of different measurement instruments or physical activity outcomes. 

Subgroup analyses revealed that the negative association between kinesiophobia and physical activity is significant in patients with cardiac, rheumatologic, neurologic, or pulmonary conditions but not in those with chronic or acute pain. This latter finding underscores the need to distinguish kinesiophobia from pain. Understanding that the fear of pain, injury, or aggravating an underlying condition, rather than actual pain, is associated with physical inactivity is important to consider when developing interventions to promote physical activity. Tailored interventions that address kinesiophobia specific to different health conditions could enhance physical activity levels and improve health outcomes. Further research is needed to explore the mechanisms underlying kinesiophobia and evaluate the efficacy of targeted interventions to mitigate its impact. 

This article makes an important contribution to our understanding of the relationship between kinesiophobia and physical activity. It provides evidence that fear of movement can be a barrier to physical activity in certain health conditions and highlights the need for condition-specific approaches to address this issue. This work is highly relevant for clinicians, researchers, and public health policymakers aiming to improve physical activity levels and overall health outcomes in a variety of populations.

References

Goubran, M., Farajzadeh, A., Lahart, I.M., Bilodeau, M. & Boisgontier, M.P. (2024). Physical activity and kinesiophobia: A systematic review and meta-analysis. MedRxiv, version. 3 peer-reviewed and recommended by Peer Community in Health and Movement Science. https://doi.org/10.1101/2023.08.17.23294240

Effective gait fundamentally requires spatial and temporal coordination of upper and lower limbs. Individuals with Parkinson’s disease (PD) often exhibit impaired coordination, leading to adverse events such as freezing of gait and falls (Plotnik et al. 2008). Despite their significance, the current literature lacks depth in our understanding of this characteristic, especially their adaptation to changing task demands and symptom laterality. Exploring these relationships may provide new insights into PD gait and facilitate the evaluation of potential treatments. With these objectives in mind, the present study conducted by Hill & Nantel (2024) includes 17 participants with mild to moderate PD and focuses on coordination within and between the more and less affected sides during both single and dual gait tasks. In the study, spatial coordination, assessed by range of motion, range of motion variability, and peak flexion for the shoulder and hip joints, was examined alongside temporal coordination, which was evaluated using the phase coordination index and variability of continuous relative phase.

Their analysis reveals that, due to dual tasking, only the shoulder range of motion and peak flexion decreased within the least affected side, adding to the existing knowledge on arm swing impairments in early-stage PD (Navarro-López et al. 2022). However, no significant difference was observed between the more and less affected sides. Hip range of motion showed dual task-related differences between sides, while lower intralimb phase variability did not. The primary strength of the article lies in its attempt to systematically explore these differences in PD. As the authors pointed out, to interpret the clinical significance of these differences as well as the null findings on temporal coordination, it may be necessary to include a healthy control group or other comparison groups, such as individuals with severe PD. When interpreting these results, readers may also pay attention to the methodological choices, such as the patient-reported most affected side and the choice of dual task. Overall, the study will be of interest to researchers studying intra- and inter-limb coordination during gait in PD.   

References

Plotnik, M., & Hausdorff, J. M. (2008). The role of gait rhythmicity and bilateral coordination of stepping in the pathophysiology of freezing of gait in Parkinson's disease. Movement disorders: official journal of the Movement Disorder Society, 23(S2), S444-S450. https://doi.org/10.1002/mds.21984 

Hill, A., & Nantel, J. (2024). Interlimb coordination in Parkinson’s Disease is minimally affected by a visuospatial dual task. bioRxiv, ver. 3 peer-reviewed and recommended by Peer Community in Health and Movement Science. https://doi.org/10.1101/2022.07.15.500215 

Navarro-Lopez, V., Fernandez-Vazquez, D., Molina-Rueda, F., Cuesta-Gomez, A., Garcia-Prados, P., del-Valle-Gratacos, M., & Carratala-Tejada, M. (2022). Arm-swing kinematics in Parkinson's disease: a systematic review and meta-analysis. Gait & Posture, 98, 85-95. https://doi.org/10.1016/j.gaitpost.2022.08.017