A single exercise bout and locomotor learning after stroke: physiological, behavioural, and computational outcomes.

KEY POINTS: Previous work demonstrated an effect of a single high-intensity exercise bout coupled with motor practice on the retention of a newly acquired skilled arm movement, in both neurologically intact and impaired adults. In the present study, using behavioural and computational analyses we demonstrated that a single exercise bout, regardless of its intensity and timing, did not increase the retention of a novel locomotor task after stroke. Considering both present and previous work, we postulate that the benefits of exercise effect may depend on the type of motor learning (e.g. skill learning, sensorimotor adaptation) and/or task (e.g. arm accuracy-tracking task, walking). ABSTRACT: Acute high-intensity exercise coupled with motor practice improves the retention of motor learning in neurologically intact adults. However, whether exercise could improve the retention of locomotor learning after stroke is still unknown. Here, we investigated the effect of exercise intensity and timing on the retention of a novel locomotor learning task (i.e. split-belt treadmill walking) after stroke. Thirty-seven people post stroke participated in two sessions, 24 h apart, and were allocated to active control (CON), treadmill walking (TMW), or total body exercise on a cycle ergometer (TBE). In session 1, all groups exercised for a short bout (∼5 min) at low (CON) or high (TMW and TBE) intensity and before (CON and TMW) or after (TBE) the locomotor learning task. In both sessions, the locomotor learning task was to walk on a split-belt treadmill in a 2:1 speed ratio (100% and 50% fast-comfortable walking speed) for 15 min. To test the effect of exercise on 24 h retention, we applied behavioural and computational analyses. Behavioural data showed that neither high-intensity group showed greater 24 h retention compared to CON, and computational data showed that 24 h retention was attributable to a slow learning process for sensorimotor adaptation. Our findings demonstrated that acute exercise coupled with a locomotor adaptation task, regardless of its intensity and timing, does not improve retention of the novel locomotor task after stroke. We postulate that exercise effects on motor learning may be context specific (e.g. type of motor learning and/or task) and interact with the presence of genetic variant (BDNF Val66Met).

The influence of high intensity exercise and the Val66Met polymorphism on circulating BDNF and locomotor learning.

Brain-derived neurotrophic factor (BDNF) has been directly related to exercise-enhanced motor performance in the neurologically injured animal model; however literature concerning the role of BDNF in the enhancement of motor learning in the human population is limited. Previous studies in healthy subjects have examined the relationship between intensity of an acute bout of exercise, increases in peripheral BDNF and motor learning of a simple isometric upper extremity task. The current study examined the role of high intensity exercise on upregulation of peripheral BDNF levels as well as the role of high intensity exercise in mediation of motor learning and retention of a novel locomotor task in neurologically intact adults. In addition, the impact of a single nucleotide polymorphism in the BDNF gene (Val66Met) in moderating the relationship between exercise and motor learning was explored. It was hypothesized that participation in high intensity exercise prior to practicing a novel walking task (split-belt treadmill walking) would elicit increases in peripheral BDNF as well as promote an increased rate and magnitude of within session learning and retention on a second day of exposure to the walking task. Within session learning and retention would be moderated by the presence or absence of Val66Met polymorphism. Fifty-four neurologically intact participants participated in two sessions of split-belt treadmill walking. Step length and limb phase were measured to assess learning of spatial and temporal parameters of walking. Serum BDNF was collected prior to and immediately following either high intensity exercise or 5min of quiet rest. The results demonstrated that high intensity exercise provides limited additional benefit to learning of a novel locomotor pattern in neurologically intact adults, despite increases in circulating BDNF. In addition, presence of a single nucleotide polymorphism on the BDNF gene did not moderate the magnitude of serum BDNF increases with high intensity exercise, nor did it moderate the relationship between high intensity exercise and locomotor learning.

Functional and physiological effects of yoga in women with rheumatoid arthritis: a pilot study.

CONTEXT: Stress, both psychological and physiological, has been implicated as having a role in the onset and exacerbations of rheumatoid arthritis (RA). OBJECTIVE: This study investigated whether neuroendocrine and physical function in women with RA can be altered through a yoga intervention. DESIGN: Exercise intervention. SETTING: University research conducted at a medical clinic. PARTICIPANTS: Sixteen independently living, postmenopausal women with an RA classification of I, II, or III according to the American College of Rheumatology functional classification system served as either participants or controls. INTERVENTION: The study group participated in three 75-minute yoga classes a week over a 10-week period. MAIN OUTCOME MEASURES: At baseline and on completion of the 10-week intervention, diurnal cortisol patterns and resting heart rate were measured. Balance was measured using the Berg Balance Test. Participants completed the Health Assessment Questionnaire (HIQ), a visual analog pain scale, and the Beck Depression Inventory. RESULTS: Yoga resulted in a significantly decreased HAQ disability index, decreased perception of pain and depression, and improved balance. Yoga did not result in a significant change in awakening or diurnal cortisol patterns (P = .12).

The effects of stress on wound healing in male tree lizards (Urosaurus ornatus).

Exposure to stress can affect an organism's partitioning of resources among immune function and other organismal functions. However, measuring immune function is often difficult. Recent studies show that the rate of cutaneous wound healing in laboratory rodents is a simple, integrated measure of stress-sensitive immune function. We investigated the use of this technique in tree lizards to test the hypotheses (1) that stress compromises wound healing and (2) that this effect is at least partially mediated by corticosterone. Laboratory-housed male tree lizards randomly assigned to the experimental and control treatment groups received a 3.5 mm cutaneous biopsy on the dorsal surface of the pelvis. Experimental group males were restrained in cloth bags for 60 min every day for 21 days during the healing profile, whereas control males were left in their cages. Wound sizes were measured every other day by image analysis. Control animals healed faster than stressed animals. The difference in wound surface area between the groups was most pronounced early in the healing profile. Stressed animals also had higher corticosterone levels and corticosterone was negatively correlated with healing rate in the stressed animals. These observations support both hypotheses that stress compromises healing and that corticosterone may act to mediate the effects of stress.

The HPA axis response to stress in women: effects of aging and fitness.

This study tested the hypotheses that aging is associated with greater hypothalamic-pituitary-adrenal (HPA) axis reactivity to psychological stress, and whether aerobic fitness is associated with a lower HPA axis response to psychological stress. Three groups, consisting of young-unfit women (27.9+/-2.5 yr, n=10), older-unfit women (66.3+/-1.4 yr, n=14), and older-fit women (66.6+/-2.0 yr, n=12), underwent the Matt Stress Reactivity Protocol (MSRP). The MSRP is a stress test battery that combines mental challenges, a physical challenge, and a psychosocial stressor. Definition of fitness was based on maximal oxygen consumption (VO(2max)) where unfit was defined as having VO(2max)average for the respective age group. The MSRP elicited increases in heart rate, blood pressure, ACTH, and cortisol (P<0.001). The older-unfit women had significantly greater cortisol responses to the challenge than both the young-unfit and the older-fit women (P<0.05), who did not differ from each other. ACTH levels were significantly higher in the older-unfit women at baseline and throughout the trial, compared to both young-unfit and the older-fit (P<0.01). The ACTH response was not different between any of the groups. The young-unfit women had greater heart rate responses than the older-unfit (P<0.01), while the latter had greater systolic blood pressure responses (P<0.01). There were no significant differences between the older-unfit and older-fit in terms of heart rate or blood pressure responses. Our result shows that among unfit women, aging is associated with greater HPA axis reactivity to psychological stress, and that higher aerobic fitness among older women can attenuate these age-related changes as indicated by a blunted cortisol response to psychological stress. These findings suggest that exercise training may be an effective way of modifying some of the neuroendocrine changes associated with aging.

Hypothalamic-pituitary-adrenal axis response and recovery from high-intensity exercise in women: effects of aging and fitness.

This study tested the hypotheses that aging is associated with prolonged recovery after a challenge to the hypothalamic-pituitary-adrenal axis (acute exercise) and that aerobic fitness is associated with a blunting of the age-related loss of negative feedback sensitivity. Young (27 +/- 2.8 yr, n = 9), older (64.6 +/- 1.4 yr, n = 11), and older-fit women (66.3 +/- 2.2 yr, n = 11) underwent a short bout of treadmill exercise at high (but submaximal) intensity. The exercise trial elicited significant increases in heart rate, blood pressure, ACTH, and cortisol (P < 0.001). Although the young and the older women exhibited similar cortisol response to the trial and throughout the recovery period, the older women had a slower decrease of ACTH levels (P < 0.05), suggesting reduced negative feedback sensitivity with aging. Between the two groups of older women, the older-fit group had significantly greater rate of recovery of ACTH levels (P < 0.05) compared with the older unfit women. However, older fit women had greater cortisol production during the recovery period (P < 0.05), suggesting greater adrenal sensitivity to ACTH. These results suggest that aging is associated with changes in the dynamic function of the hypothalamic-pituitary-adrenal axis and that these changes are attenuated by aerobic fitness.

Effects of the oral contraceptive pill cycle on physiological responses to hypoxic exercise.

To test whether the oral contraceptive pill cycle affects endocrine and metabolic responses to hypoxic (fraction of inspired oxygen = 13%, P(IO2): 95 mmHg; H) versus normoxic (P(IO2):153 mmHg; N) exercise, we examined eight women (28 +/- 1.2 yr) during the third (PILL) and placebo (PLA) weeks of their monthly oral contraceptive pill cycle. Cardiopulmonary, metabolic, and neuroendocrine measurements were taken before, during, and after three 5-min consecutive workloads at 30%, 45%, and 60% of normoxic V(O2peak) in H and N trials. Heart rate response to exercise was greater in H versus N, but was not different between PILL and PLA. Lactate levels were significantly greater during exercise, and both lactate and glucose levels were significantly greater for 30 min after exercise in H versus N (p < 0.0001). When expressed relative to baseline, lactate levels were lower in PILL versus PLA, but glucose was greater in PILL versus PLA (p < 0.001). Cortisol levels were also significantly greater in PILL versus PLA (p < 0.001). Norepinephrine levels were significantly increased during exercise (p < 0.0001) and in H versus N (p < 0.0001). However, epinephrine levels were not different over time or with trial. Thus, the presence of circulating estradiol and progesterone during the PILL phase reduces glucose and lactate responses to hypoxic exercise.

Gender differences in the endocrine and metabolic responses to hypoxic exercise.

This study tested the hypothesis that women would have blunted physiological responses to acute hypoxic exercise compared with men. Fourteen women taking oral contraceptives (28 +/- 0.9 yr of age) and 15 men (30 +/- 1.0 yr of age) with similar peak O(2) consumption (VO(2 peak)) values (56 +/- 1.1 vs. 57 +/- 0.8 ml x kg fat-free mass(-1) x min(-1)) were studied under hypoxic (H; fraction of inspired oxygen = 13%) vs. normoxic (fraction of inspired oxygen = 20.93%) conditions. Cardiopulmonary, metabolic, and neuroendocrine measures were taken before, during, and 30 min after three 5-min consecutive workloads at 30, 45, and 60% VO(2 peak). In women compared with men, glucose levels were greater during recovery from H (P < 0.05) and lactate levels were lower at 45% VO(2 peak), 60% VO(2 peak), and up to 20 min of recovery (P < 0.05), regardless of trial (P < 0.0001). Although the women had greater baseline levels of cortisol and growth hormone (P < 0.0001), gender did not affect these hormones during H or exercise. Catecholamine responses to H were also similar between genders. Thus the endocrine response to hypoxia per se was not blunted in women as we had hypothesized. Other mechanisms must be at play to cause the gender differences in metabolic substrates in response to hypoxia.