Aging and balance control in response to external perturbations: role of anticipatory and compensatory postural mechanisms

Abstract

The ability to maintain balance deteriorates with increasing age. Anticipatory and compensatory postural adjustments (APAs and CPAs, respectively), both, are known to be affected in the elderly. We examined the effect of aging on the ability of older adults to utilize APAs and its effect on subsequent control of posture (CPAs). Ten elderly individuals were exposed to external predictable and unpredictable perturbations applied to the upper body in the sagittal plane. Body kinematics, electromyographic activity of 13 muscles, and ground reaction forces were analyzed during the anticipatory and compensatory phases of postural control. The elderly were capable of recognizing an upcoming predictable perturbation and activated muscles prior to it. However, the older adults used different muscle strategies and sequence of muscle recruitment than that reported in young adults. Additionally, when the perturbations were unpredictable, no APAs were seen which resulted in large CPAs and greater peak displacements of the center of pressure (COP) and center of mass (COM) following perturbations. As opposed to this, when the perturbations were predictable, APAs were seen in older adults resulting in significantly smaller CPAs. The presence and utilization of APAs in older adults also improved postural stability following the perturbation as seen by significantly smaller COP and COM peak displacements. Using APAs in older adults significantly reduces the need for large CPAs, resulting in greater postural stability following a perturbation. The results provide a foundation for investigating the role of training in improving the interplay between anticipatory and compensatory postural control in older adults.

Fig. 1

Muscle activity onsets for dorsal (a) and ventral (b) muscles. Note that for predictable perturbations the onset of muscle activity occurred prior to the perturbation (T ₀). In case of unpredictable perturbations, the muscle onsets occurred after the perturbation. Dorsal muscles: SOL (soleus), GASL (lateral gastrocnemius), GASM (medial gastrocnemius), BF (biceps femoris), ST (semitendinosus), and ESL (erector spinae longus). Ventral muscles: TA (tibilais anterior), RF (rectus femoris), VM (vastus medialis), VL (vastus lateralis), EO (external oblique), and RA (rectus abdominis). Differences in latencies between predictable and unpredictable conditions are significant for all muscles shown, p < 0.01

Fig. 2

Normalized integrated EMG activities in older adults during the four epochs (APA1, APA2, CPA1, and CPA2) are shown for the ventral muscles: RA (rectus abdominis), VL (vastus lateralis), VM (vastus medialis), RF (rectus femoris), and TA (tibialis anterior). Positive values indicate an activation of the muscle, while negative values indicate a muscle inhibition. *p < 0.01 and **p < 0.001

Fig. 3

Normalized integrated EMG activities in older adults during the four epochs (APA1, APA2, CPA1, and CPA2) are shown for the lateral muscles: GMED (gluteus medius) and EO (external oblique). Positive values indicate an activation of the muscle, while negative values indicate a muscle inhibition. **p < 0.001

Fig. 4

Displacements of COP (a) and COM (b) at T ₀ (anticipatory) and peak displacements (after T ₀, compensatory) for predictable and unpredictable perturbations are shown. Positive values indicate displacement in the posterior/backward direction and negative values indicate displacement in the anterior/forward direction. **p < 0.001 and *p < 0.05