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When we trip, slip or miss-step, we do not give any thought to the complicated processes occurring as our leg swings through the air and after our foot contacts the ground. This entire response happens rapidly, within milliseconds. Interestingly, for many years, researchers chose to truncate their studies of reactive stepping at the moment the foot hit the ground. However, more recently researchers have begun to investigate the landing phase of reactive stepping, which occurs after foot-contact.

Studying balance control after the foot contacts the ground is very important because studies of real-life falls in older adults in long-term care have revealed that incorrect weight shifting was the largest cause of falls in these older adults [1]. This finding shows that our stability is not guaranteed just because both feet are on the ground, and we still must control our body movement effectively.

From a mechanical perspective, the requirements of the stepping leg do not become critical until after foot landing, when the angular momentum of the body must be counteracted via the generation of forces and moments (rotational forces) [2]. The recovery limb is capable of generating a moment that will counteracts the body’s forward rotation if placed in front of the body’s center of mass (COM) [3].

The landing phase is particularly important for the maintenance of dynamic stability because it may have the most direct influence on the kinematics of the COM after movement initiation when the swing phase is complete, and the foot is back in contact with the ground [4]. The notion that multiple researchers have reported that older adults used more than one step to recover their balance in response to externally applied laboratory perturbations suggests that older adults may have impairments in their balance that occur after landing of the first step [4-7]. Future blogs will explore these age-related changes after foot-contact.

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[1] Robinovitch, S. N., Feldman, F., Yang, Y., Schonnop, R., Leung, P. M., Sarraf, T., Sims-Gould, J., & Loughin, M. (2013). Video capture of the circumstances of falls in elderly people residing in long-term care: an observational study. Lancet (London, England), 381(9860), 47–54. https://doi.org/10.1016/S0140-6736(12)61263-X

[2] Pijnappels M, Bobbert MF, van Dieën JH. Contribution of the support limb in control of angular momentum after tripping. J Biomech. 2004 Dec;37(12):1811-8. doi: 10.1016/j.jbiomech.2004.02.038. PMID: 15519588.

[3] Grabiner MD, Koh TJ, Lundin TM, Jahnigen DW. Kinematics of recovery from a stumble. J Gerontol. 1993 May;48(3):M97-102. doi: 10.1093/geronj/48.3.m97. PMID: 8482818.

[4] Singer JC, Prentice SD, McIlroy WE. Dynamic stability control during volitional stepping: a focus on the restabilisation phase at movement termination. Gait Posture. 2012 Jan;35(1):106-10. doi: 10.1016/j.gaitpost.2011.08.018. Epub 2011 Oct 21. PMID: 22018700.

[5] Schulz BW, Ashton-Miller JA, Alexander NB. Compensatory stepping in response to waist pulls in balance-impaired and unimpaired women. Gait Posture. 2005 Nov;22(3):198-209. doi: 10.1016/j.gaitpost.2004.09.004. Epub 2004 Nov 5. PMID: 16214659.

[6] Luchies CW, Alexander NB, Schultz AB, Ashton-Miller J. Stepping responses of young and old adults to postural disturbances: kinematics. J Am Geriatr Soc. 1994 May;42(5):506-12. doi: 10.1111/j.1532-5415.1994.tb04972.x. PMID: 8176145.

[7] McIlroy WE, Maki BE. Age-related changes in compensatory stepping in response to unpredictable perturbations. J Gerontol A Biol Sci Med Sci. 1996 Nov;51(6):M289-96. doi: 10.1093/gerona/51a.6.m289. PMID: 8914501.