The effects of foot cooling on postural muscle responses to an unexpected loss of balance

Effects of increasing temperature in different foot regions on foot sensitivity and postural control in young adults

Despite controversial evidence, foot sensitivity may influence postural control. Since skin temperature changes may induce changes in skin sensitivity, it remains unclear whether this also affects postural control. Here we examined the effects of increasing foot temperature on foot sensitivity and postural control responses. It is hypothesized that increases in foot temperature would improve foot sensitivity and enhance postural control. Furthermore, it was investigated whether warming a larger foot area provides additional benefits. Our hypothesis was tested by warming the foot plantar and the whole foot and ankle area (including foot plantar and instep) using infrared radiation and evaluated the center of pressure (CoP, bilateral, in two conditions: eyes open and eyes closed) and foot tactile sensitivity (Semmes-Weinstein Monofilaments) in 22 young participants. Both warming protocols significantly increased foot temperature by ∼5-6 °C and improved sensitivity, whereas more considerable improvements happened after warming the whole foot and ankle. CoP mediolateral oscillation and velocity with eyes open, and CoP area and velocity with eyes closed reduced after both warming protocols. Foot sensitivity seems to depend on the foot area warmed, whereas postural control improved equally regardless of the warmed regions. These results may support interventions based on the manipulation of foot temperatures to improve postural control with potential clinical applications in populations with impaired foot sensitivity and balance.

SC, Crews RT. Diabetes and Reactive Balance: Quantifying Stepping Thresholds With a Simple Spring Scale to Measure Fall-Risk in Ambulatory Older Adults

BACKGROUND

Fall-risk assessments for patients with diabetes fail to consider reactive responses to balance loss. The purpose of this study was to assess the feasibility of using a simple clinical tool to evaluate the impact of diabetes and fall history on reactive balance in older adults.

METHODS

We recruited 72 older adults with and without diabetes. Postural perturbations were applied by a waist-mounted spring scale. Stepping thresholds (STs) in the anterior and posterior directions were defined as the lowest spring-loads that induced a step. Balance was assessed via the National Institutes of Health Toolbox Standing Balance Test, and lower extremity sensation was assessed using vibratory perception threshold and Semmes-Weinstein monofilaments. Fall history over the past year was self-reported. Cox regressions and analysis of variance were used to compare hazard rates for stepping and observed STs between groups.

RESULTS

Anterior STs were elicited in 42 subjects and posterior STs in 65 subjects. Hazard rates for posterior ST were significantly affected by diabetes, with greater hazards for fallers with diabetes versus control fallers and nonfallers, after accounting for balance and sensory loss. For those who stepped, ST was lower in the posterior direction for the diabetes group. Additionally, anterior but not posterior ST was lower in all fallers vs all nonfallers.

CONCLUSIONS

The waist-mounted spring scale is a clinically implementable device that can assess ST in older adults with diabetes. Using the device, we demonstrated that ST was affected by diabetes and could potentially serve as a fall-risk factor independent of balance or sensory loss.

Cutaneous and muscular afferents from the foot and sensory fusion processing: Physiology and pathology in neuropathies

The foot-sole cutaneous receptors (section 2), their function in stance control (sway minimisation, exploratory role) (2.1), and the modulation of their effects by gait pattern and intended behaviour (2.2) are reviewed. Experimental manipulations (anaesthesia, temperature) (2.3 and 2.4) have shown that information from foot sole has widespread influence on balance. Foot-sole stimulation (2.5) appears to be a promising approach for rehabilitation. Proprioceptive information (3) has a pre-eminent role in balance and gait. Reflex responses to balance perturbations are produced by both leg and foot muscle stretch (3.1) and show complex interactions with skin input at both spinal and supra-spinal levels (3.2), where sensory feedback is modulated by posture, locomotion and vision. Other muscles, notably of neck and trunk, contribute to kinaesthesia and sense of orientation in space (3.3). The effects of age-related decline of afferent input are variable under different foot-contact and visual conditions (3.4). Muscle force diminishes with age and sarcopenia, affecting intrinsic foot muscles relaying relevant feedback (3.5). In neuropathy (4), reduction in cutaneous sensation accompanies the diminished density of viable receptors (4.1). Loss of foot-sole input goes along with large-fibre dysfunction in intrinsic foot muscles. Diabetic patients have an elevated risk of falling, and vision and vestibular compensation strategies may be inadequate (4.2). From Charcot-Marie-Tooth 1A disease (4.3) we have become aware of the role of spindle group II fibres and of the anatomical feet conditions in balance control. Lastly (5) we touch on the effects of nerve stimulation onto cortical and spinal excitability, which may participate in plasticity processes, and on exercise interventions to reduce the impact of neuropathy.

Sensory-to-Motor Overflow: Cooling Foot Soles Impedes Squat Jump Performance

Evidence from recent studies on animals and humans suggest that neural overflow from the primary sensory cortex (S1) to the primary motor cortex (M1) may play a critical role in motor control. However, it is unclear if whole-body maximal motor tasks are also governed by this mechanism. Maximum vertical squat jumps were performed by 15 young adults before cooling, then immediately following a 15-min cooling period using an ice-water bath for the foot soles, and finally immediately following a 15-min period of natural recovery from cooling. Jump heights were, on average, 3.1 cm lower immediately following cooling compared to before cooling (p = 3.39 × 10⁻⁸) and 1.9 cm lower following natural recovery from cooling (p = 0.00124). The average vertical ground reaction force (vGRF) was also lower by 78.2 N in the condition immediately following cooling compared to before cooling (p = 8.1 × 10⁻⁵) and 56.7N lower following natural recovery from cooling (p = 0.0043). The current study supports the S1-to-M1 overflow mechanism in a whole-body dynamic jump.

Associations Between Women's Obesity Status and Diminished Cutaneous Sensibility Across Foot Sole Regions

People who are obese sustain very high foot pressures when standing, with potential consequences to their feet soles' cutaneous sensibility. In the current investigation, we performed a detailed assessment of foot sole sensibility in women with morbid obesity (n = 13; age = 38.85, SD = 8.09 years) status in comparison with leaner women (n = 13; age = 37.62, SD = 7.10 years). We estimated tactile feet sole sensibility through graduated monofilament light touch applied at several hotspots of both feet soles, covering the toes, metatarsal heads, midfoot internal and lateral arches, and heel. Intergroup comparisons per foot sole region indicated significantly lower sensibility for the group with morbid obesity under the fifth and third metatarsal heads, midfoot lateral and internal arches and heel. We found a large variation across the sole regions, with the lowest difference between the obese and lean groups observed under the hallux (18%) and the largest difference observed under the lateral arch of the midfoot (76%). Correlation analyses between body weight and sensibility scores revealed a significant positive correlation among participants who were leaner (r_s = 0.56, p = 0.05) but not among participants who were obese (r_s = -0.06, p = 0.83). Mainly, our results showed that morbid obesity was associated with significantly higher cutaneous sensibility thresholds, with large variability of the sensibility deficit across different regions of both feet soles. Due to its functional relevance for body balance control, reduced sensibility thresholds among women who are morbidly obese may have implications for stance stability.

Human Balance in Response to Continuous, Predictable Translations of the Support Base: Integration of Sensory Information, Adaptation to Perturbations, and the Effect of Age, Neuropathy and Parkinson’s Disease

This short narrative review article moves from early papers that described the behaviour of healthy subjects balancing on a motorized platform continuously translating in the antero-posterior direction. Research from the laboratories of two of the authors and related investigations on dynamic balancing behaviour are briefly summarized. More recent findings challenging time-honoured views are considered, such as the statement that vision plays a head-in-space stabilizing role. The time interval to integrate vision or its withdrawal in the balancing pattern is mentioned as well. Similarities and differences between ageing subjects and patients with peripheral or central disorders are concisely reported. The muscle activities recorded during the translation cycles suggest that vision and amplitude changes of the anticipatory postural activities play a predominant role in controlling dynamic balance during prolonged administration of the predictable perturbation. The potential of this paradigm for rehabilitation of balance problems is discussed.