Do cross-education effects last over time?

Recent studies have unveiled a fascinating aspect of our bodily interconnectedness. Specifically, these investigations have delved into the effects of stretching and foam rolling, not only on the localised region being addressed, but on distant parts of the body as well. The researchers unearthed evidence suggesting that engaging in these practices on one side of the body can yield significant improvements in range of motion for the contralateral side. This phenomenon - called the cross-education effect - was observed over a period of several weeks, pointing to a deeper level of bodily integration that these activities tap into [1-4].

When we train a particular muscle group, it's not only the targeted fibres that reap the benefits; the corresponding muscles on the opposite side of our body also experience improvements, underscoring the brain's sophisticated control mechanisms that govern bilateral symmetry and function. The cross-education effect is underpinned by the brain's adeptness at organising and coordinating muscular activity, fostering a harmonious operation of analogous muscle groups on either side of our body.

Thus, when we advance in one aspect - be it through enhancing our flexibility, endurance, or pain threshold within a specific muscle group - the group on the contralateral side witnesses a parallel enhancement. It’s as if the brain maintains a blueprint for muscular function that applies a universal improvement policy, notwithstanding the direct physical engagement of both sides.

However, we must remember to distinguish between the neurological adaptations and the actual structural changes within the muscle tissue. While the former can indeed occur through this indirect training effect, the latter - specific changes in muscle stiffness or morphology - remain elusive without direct intervention. This distinction was highlighted in research findings that illustrated how stretching one side of the body could increase flexibility on the other, without altering the intrinsic stiffness of the muscles involved [2].

It appears that the improvements observed in the flexibility on the contralateral side of the body - the side not directly engaged in the stretching exercise - cannot be attributed to any reduction in muscular stiffness or alterations in the muscular structure itself. Rather, these effects are borne of an interaction between the brain and the peripheral nervous system, leading to enhanced stretch tolerance.

Studies have differentiated between the mechanical changes within the muscle tissue - commonly expected outcomes like decreased stiffness and increased muscle length from prolonged stretching exercises - and neural adaptations [5,6]. This distinction is important. On the side of the body directly involved in stretching, such mechanical changes are indeed observable. However, on the opposite side, which does not undergo the same physical stretching or rolling, the observed increase in flexibility suggests a different mechanism at play. It indicates a capacity for our nervous system to adapt and reconfigure its responses, leading to improved flexibility without direct mechanical intervention on the muscle tissue.

This insight underscores the plasticity of the human body, emphasising that our physical capabilities and improvements are not only the result of changes in muscle structure. Instead, they are deeply intertwined with the ways in which our brains and nerves communicate and adapt to different stimuli.

Yet, recent studies should temper optimism for contralateral effects of stretching and foam rolling [7,8]. They suggest that the chronic benefits of enhancing flexibility in untreated body segments through stretching and foam rolling may not hold empirical water. Thus, while immediate gains in flexibility on the opposing side of the body might be observable post-stretch or -roll, these improvements appear to be ephemeral, dissipating with the continuation of these practices over time. Eventually, the effects on the opposite (untrained) side of the body decrease because the nervous system adapts and reaches a point where it doesn't improve much further.

To develop serious levels of flexibility in a particular joint, engaging in stretching exercises or utilising a foam roller on the associated muscle(s) is necessary. Of course, we can achieve this without traditional stretching or foam rolling. It's here that the work of Alizadeh et al. becomes illuminating [9]. They demonstrated that resistance training - executed with a commitment to the full range of motion - promises an incremental gain in the joint's flexibility over time and also confers a suite of auxiliary benefits. This approach enhances muscle strength and size, mitigates back discomfort, and fortifies cardiovascular health.

References

1. Moltubakk, M. et al. (2021) 'Altered triceps surae muscle-tendon unit properties after 6 months of static stretching.' Medicine and Science in Sports and Exercise, volume 53, pages 975-986.
2. Nakamura, M. et al. (2022) 'Cross-education effect of 4-week high- or low-intensity static stretching intervention programs on passive properties of plantar flexors.' Journal of Biomechanics, volume 133, article 110958.
3. Panidi, I. et al. (2021) 'Muscle architectural and functional adaptations following 12-weeks of stretching in adolescent female athletes.' Frontiers in Physiology, article 1088.
4. Kasahara, K. et al. (2022) 'Comparison between 6-week foam rolling intervention program with and without vibration on rolling and non-rolling sides.' European Journal of Applied Physiology, volume 122, pages 2061-2070.
5. Takeuchi, K. et al. (2023) 'Long-term static stretching can decrease muscle stiffness: a systematic review and meta-analysis.' Scandinavian Journal of Medicine and Science in Sports, volume 33, pages 1294-1306.
6. Panidi, I. et al. (2023) Muscle architecture adaptations to static stretching training: a systematic review with meta-analysis.' Sports Medicine Open, volume 9, article 47.
7. Konrad, A. et al. (2023) 'Remote effects of a 7-week combined stretching and foam rolling training intervention of the plantar foot sole on the function and structure of the triceps surae.' European Journal of Applied Physiology, volume 123, pages 1645-1653.
8. Konrad, A. et al. (2024) 'The non-local effects of 7-week foot sole static stretching and foam rolling training on shoulder extension range of motion.' Frontiers in Sports and Active Living, volume 5, article 1335872.
9. Alizadeh, S. et al. (2023) 'Resistance training induces improvements in range of motion: a systematic review and meta-analysis.' Sports Medicine, volume 53, pages 707-722.