Ronald H. Cox

A differential catecholamine response during prolonged exercise and passive heating.

Plasma catecholamines (Ca) increase over time during prolonged exercise at a constant work rate. Possible reasons for this include hypoglycemia, dehydration, increased perceived exertion, and rising body temperature. In an effort to ascertain the contribution of elevated core temperature on the plasma Ca response to prolonged exercise four trained men were studied under two thermal conditions during 45 min of bicycle exercise (approximately 60% Vo2max) and during passive heating. On one testing day each subject was heat-stressed during exercise wearing a nylon pullover shell and cotton pants, (heat stress treatment); on the second day fans were directed on the subjects exercising in a thermoneutral environment (fan treatment). The passive heating experiment was conducted in a hot water bath (41 degrees C). The exercise heat stress treatment produced a higher plasma norepinephrine (NE) concentration (P less than 0.05) in all subjects than the fan treatment. The plasma epinephrine (E) concentration was not significantly (P greater than 0.05) different during exercise in the heat stress treatment from that found during fan treatment. A rise in rectal temperature (Tre) during passive heating resulted in quantitatively small changes in plasma E and NE. The heat load combined with the exercise task produced an increase in plasma NE concentration greater than the sum of the values measured during exercise in the thermoneutral environment and passive heating. This suggested that the combination of stressors caused an augmentation of the sympathetic nervous systems response. Finally, the added heat load caused changes in plasma NE and little change in plasma E, suggesting a differential Ca response with heat stress.

The Acute Effects of Static Stretching on the Sprint Performance of Collegiate Men in the 60- and 100-m Dash After a Dynamic Warm-Up

Kistler, BM, Walsh, MS, Horn, TS, and Cox, RH. The acute effects of static stretching on the sprint performance of collegiate men in the 60- and 100-m dash after a dynamic warm-up. J Strength Cond Res 24(9): 2280-2284, 2010-Previous research has shown that static stretching has an inhibitory effect on sprinting performances up to 50 m. The purpose of this study was to see what would happen to these effects at longer distances such as those seen in competition. This study used a within-subjects design to investigate the effects of passive static stretching vs. no stretching on the 60- and 100-m sprint performance of college track athletes after a dynamic warm-up. Eighteen male subjects completed both the static stretching and the no stretching conditions in counterbalanced order across 2 days of testing. On each day, all subjects first completed a generalized dynamic warm-up routine that included a self-paced 800-m run, followed by a series of dynamic movements, sprint, and hurdle drills. At the end of this generalized warm-up, athletes were assigned to either a static stretching or a no-stretching condition. They then immediately performed 2 100-m trials with timing gates set up at 20, 40, 60, and 100 m. Results revealed a significant slowing in performance with static stretching (p < 0.039) in the second 20 (20-40) m of the sprint trials. After the first 40 m, static stretching exhibited no additional inhibition of performance in a 100-m sprint. However, although there was no additional time loss, athletes never gained back the time that was originally lost in the first portion of the trials. Therefore, in strict terms of performance, it seems harmful to include static stretching in the warm-up protocol of collegiate male sprinters in distances up to 100 m.

Exercise training and response to stress: Insights from an animal model.

The effect of training on the sympathoadrenal and cardiovascular responses to stress was examined in borderline hypertensive rats (BHRs). Animals trained with swimming showed reduced heart rates and plasma norepinephrine and epinephrine levels in response to novel foot shock stress. In contrast, systolic blood pressure was significantly higher in trained BHRs during the stress. Parasympathetic blockade with atropine sulfate (1 mg.kg-1 IV) had little effect on heart rate during stress in untrained rats but significantly elevated the stress-induced heart rate of trained animals. The reduction in stress reactivity produced by exercise training is not manifested in all physiological variables and increases in parasympathetic tone contribute strongly to the attenuated reactivity in heart rate.

Effect of walking speed on typing performance using an active workstation.

This study tested the effect of treadmill walking speed on typing performance when these tasks were performed simultaneously. 24 research participants (M age = 23.2 yr.) performed a typing test under each of four conditions including the control (seated), treadmill walking at 1.3 km/hr., 2.25 km/hr., and 3.2 km/hr. Results indicated that treadmill walking had a detrimental effect on typing performance, but that the walking speed of 2.25 km/hr. would result in better typing performance than the slower and faster speeds. Seated typing was better than typing while walking at 1.3 km/hr. and typing while walking at 3.2 km/hr. Typing performance while walking at 2.25 km/hr. was not different than seated typing performance. The results support the potential of treadmill walking at 2.25 km/hr. to provide low-intensity physical activity without compromising typing performance.

Bilateral renal denervation can prevent the development of stress-induced hypertension in the borderline hypertensive rat

The borderline hypertensive rat (BHR) shows large blood pressure responses to either stress or a high salt diet. Since the renal nerves have been shown to play a role in several animal models of hypertension, the current study sought to determine the effect of bilateral renal denervation on the development of stress-induced hypertension in the BHR. BHR were deprived of renal nerves under ether anesthesia after either 5 or 11 weeks of daily 2-hour stress sessions. Additional BHR received sham surgery. Unstressed BHR, age-matched to stressed groups, received denervation or sham surgery. Following a 3 week recovery period, the protocol (stress or no stress) was continued for 10 additional weeks. Tail cuff systolic blood pressures were obtained weekly. BHR stressed for 5 weeks prior to denervation failed to develop hypertension in response to continued stress. Although BHR stressed for 11 weeks prior to denervation showed a temporary reduction in pressure following denervation, blood pressure returned to the hypertensive levels of sham-operated controls after several weeks. Thus, there may be a critical period during which the renal nerves are necessary for the expression of stress-induced hypertension in the BHR. These observations are discussed in relation to the effects of renal denervation on hypertension in various animal models.

Training history constrains postural sway dynamics: A study of balance in collegiate ice hockey players

BACKGROUND Balance and postural control are integral to training and sport performance. Demands on posture are contextual and vary in different ways depending on the specific physical activity. RESEARCH QUESTION The purpose of this study was to examine the possibility that sustained exposure to environmental constraints, through specific sport participation, might lead to a persistent modification of postural control. METHODS Double and single-leg postural sway were compared between ice hockey players, American football players and physically active college students. Data from 30 s trials were analyzed using traditional postural sway measures of range and pathlength of the center of pressure, as well as with Sample Entropy (SEn), in both mediolateral (ML) and anteroposterior (AP) directions. RESULTS Each group displayed unique postural sway characteristics. During single-leg stance, ice hockey players show significantly different ML pathlength and ML and AP SEn from the physically active college students (all p < 0.05), and significantly different ML and AP pathlength and AP SEn from the American football players (all p < 0.05). The American football players and the physically active college students differed for all single-legged conditions (all p < 0.05). SIGNIFICANCE This suggests that the organization and development of postural sway is not only context dependent but also influenced by training history; supporting the idea that balance training for sport should be designed with regards to sport specific conditions.