Thelma S. Horn

Plasma catecholamine response to acute psychological stress in humans : relation to aerobic fitness and exercise training

Existing cross-sectional studies on plasma catecholamine activity provide no support for the concept that a markedly high level of aerobic fitness modifies sympathoadrenal response to an acute psychological challenge in humans. In contrast, compromised sympathetic nervous system activity has been observed in individuals with low aerobic fitness and the relationship probably reflects a global deconditioning syndrome involving both psychological and physiological processes. The relationship between low levels of fitness and plasma norepinephrine may appear as a blunted or augmented response depending upon the nature of the task. Short-term (3-4 months) exercise training studies conducted with humans have not indicated a substantial adaptation in the relative plasma catecholamine change from a preexisting baseline during exposure to acute psychological stress. Exercise training can lower basal circulating plasma norepinephrine, resulting in lower absolute concentrations during an acute challenge, but the studies in this area lack consistency and the absolute change tends to be modest. There is no evidence that fitness or exercise training is significantly associated with plasma epinephrine activity during short-term psychological 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.

Prevalence of metabolic syndrome risk factors in high school and NCAA division I football players.

Abstract Steffes, GD, Megura, AE, Adams, J, Claytor, RP, Ward, RM, Horn, TS, and Potteiger, JA. Prevalence of metabolic syndrome risk factors in high school and NCAA Division I football players. J Strength Cond Res 27(7): 1749–1757, 2013—Metabolic syndrome (MetSyn) is a clustering of metabolic and cardiovascular disease risk factors. The purpose of this study was to determine the prevalence of MetSyn risk factors in high school (HS) and college (College) football players and to examine if the prevalence varied according to body fat percent (%Fat). One hundred twenty-three males (height 179.0 ± 6.7 cm; weight 89.4 ± 19.6 kg) from 7 different high schools and 82 males (height 186.2 ± 6.8 cm; weight 99.6 ± 16.8 kg) from one university participated. All testing occurred in the early morning after an overnight fast. %Fat, waist circumference, resting systolic and diastolic blood pressure, fasting triglyceride, high-density lipoprotein (HDL) cholesterol, and blood glucose were determined using standard testing procedures. The MetSyn risk factor levels were determined using American Heart Association criteria. Subjects were grouped by position and playing level (HS, College). Independent t-tests, chi-square analysis, 2-way analysis of variance, and path analytic models were used in the statistical analysis. Significance was set at p < 0.05. 6.8% (n = 14) of the sample met the American Heart Association criteria for MetSyn. Offensive and defensive linemen accounted for 92.3% of the players meeting MetSyn criteria with each playing level (HS, College) having 7 subjects. The MetSyn criteria differed significantly across %Fat. Obese players were more likely to meet the criteria for MetSyn. %Fat was a statistically significant predictor of mean arterial blood pressure, HDL cholesterol, and waist circumference. The MetSyn exists in both HS- and College-level football players, with almost all cases occurring in the athletes with the highest levels of %Fat (offensive/defensive lineman). Strength and conditioning coaches should be aware of the prevalence of MetSyn risk factors in offensive and defensive linemen and take appropriate actions to ensure athlete safety.

Heart rate monitoring as a measure of physical activity in children

PURPOSE Using a larger sample and broader range of activities than most previous investigations of HR monitoring, this study examined the need for individual calibration of the HR-VO2 prediction equation, the effect of including low-intensity activities when establishing the HR-VO2 equation, comparisons of different methods for calculating HR-VO2 prediction equations for maximum energy expenditure (EE) variance, and the effect of these different methods when applied to free-living HR data. METHODS Forty-three children ages 8 to 12 completed laboratory assessments of the relationship between HR and VO2. Different methods of estimating daily EE were applied to free-living HR data collected from 37 of these children. RESULTS There was significant individual variation in the HR-VO2 prediction equations. HR monitoring predicted VO2 during low-intensity activities, below most established cut points. Individual differences persisted during both high- and low-intensity activities. Although a HR-VO2 prediction equation generated from the group accounted for 85% of the variance in EE, significant improvements in prediction were achieved with individualized HR-VO2 prediction equations that took into account low-intensity activity levels. CONCLUSION Generic equations derived from group data may be suitable for some applications. However, for investigators requiring more precision, individual HR-VO2 equations significantly improve prediction.

Selected psychophysiological stress responses in men with high and low body fatness.

Previous research on catecholamine (CA) response to exercise has linked heightened adiposity to a hypostress syndrome. In the present study a cognitive/psychomotor stressor was employed to determine whether this association exists during less metabolically challenging tasks. Moreover, because stress is manifested in a multidimensional manner, measures of behavior and perceived distress were analyzed in addition to the physiological response. Men were selectively recruited for two body fatness groups (low, 12 +/- 4%, N = 9; high, 27 +/- 2%, N = 10) while being matched on age, lean weight, and peak absolute oxygen consumption. All men performed a modified Stroop task for 12 min to induce a psychophysiological stress response. Physiological changes included significant increases in heart rate, venous plasma norepinephrine, and epinephrine. Cognitive/psychomotor responses indicated no change in reaction time during the task but significant cognitive fatigue as indicated by post-task anagram performance. Perceived distress was suggested by elevated state anxiety. The high and low adiposity groups were similar on all measures of the psychophysiological stress response. These findings suggest that elevated adiposity is not characterized by a hypostress state during the relatively low metabolic challenge of a cognitive/psychomotor stressor.