Fred W. Kolkhorst

Translating physical activity recommendations into a pedometer-based step goal: 3000 steps in 30 minutes.

BACKGROUND It is a public health recommendation to accumulate at least 150 minutes per week of moderate intensity physical activity. Although pedometers are widely used as a physical activity-monitoring tool, they are unable to measure activity intensity. Translating current physical activity recommendations into a pedometer-based guideline could increase the public health impact of physical activity interventions. METHODS A community sample of 97 adults (60% women, with a mean age of 32.1 [+/-10.6] years and a mean BMI of 28.8 [+/-5.5]) completed four 6-minute incremental walking bouts on a level treadmill at 65, 80, 95, and 110 m x min(-1). A calibrated metabolic cart was used to measure energy expenditure at each speed. Steps were measured using a Yamax SW-200 pedometer. Step-rate cut points associated with minimally moderate-intensity activity (defined as 3 METs) were determined using multiple regression, mixed modeling, and receiver operating characteristic (ROC) curves. All data were collected and analyzed in 2006. RESULTS For men, step counts per minute associated with walking at 3 METs were 92 step x min(-1) (multiple regression); 101 step x min(-1) (mixed modeling); and 102 step x min(-1) (ROC curve). For women, step counts per minute associated with walking at 3 METs were 91 step x min(-1) (multiple regression); 111 step x min(-1) (mixed modeling); and 115 step x min(-1) (ROC curve). However, for each analysis there was substantial error in model fit. CONCLUSIONS Moderate-intensity walking appears approximately equal to at least 100 step x min(-1). However, step counts per minute is a poor proxy for METs, and so 100 step x min(-1) should be used only as a general physical activity promotion heuristic. To meet current guidelines, individuals are encouraged to walk a minimum of 3000 steps in 30 minutes on 5 days each week. Three bouts of 1000 steps in 10 minutes each day can also be used to meet the recommended goal.

Metabolic demands of simulated firefighting tasks.

Firefighters having higher cardiovascular fitness completed a series of simulated firefighting tasks more quickly than those having lower fitness. These results support the need of a high level of cardiovascular fitness for firefighters to ensure not only their safety, but that of fellow firefighters and rescue victims.

Physiologic Effects of the TASER After Exercise

OBJECTIVES Incidents of sudden death following TASER exposure are poorly studied, and substantive links between TASER exposure and sudden death are minimal. The authors studied the effects of a single TASER exposure on markers of physiologic stress in humans. METHODS This prospective, controlled study evaluated the effects of a TASER exposure on healthy police volunteers after vigorous exercise, compared to a subsequent, identical exercise session that was not followed by TASER exposure. Subjects exercised to 85% of predicted heart rate (HR) on an ergometer and then were given a standard 5-second TASER activation. Measures before and for 60 minutes after the TASER activation included minute ventilation, tidal volume, respiratory rate, end-tidal pCO(2), oxygen saturation, HR, blood pressure (systolic BP/diastolic BP), 12-lead electrocardiogram, and arterialized blood for pH, pO(2), pCO(2), and lactate. Each subject repeated the exercise and data collection session on a subsequent data, without TASER activation. Data were analyzed using paired Students t-tests with differences and 95% confidence intervals (CIs). Statistical significance was adjusted for multiple comparisons. RESULTS A total of 25 officers (21 men and 4 women) completed both portions of the study. After adjusting for multiple comparisons, the TASER group was significantly higher for systolic BP at baseline (difference of 14.1, 95% CI = 8.7 to 19.5, p < 0.001) and HR at 5, 30, and 60 minutes with the largest difference at 30 minutes (difference of 7.0, 95% CI = 2.5 to 11.5, p = 0.004). There were no other significant differences between the two groups in any other measure at any time. CONCLUSIONS A 5-second exposure of a TASER following vigorous exercise to healthy law enforcement personnel does not result in clinically significant changes in ventilatory or blood parameters of physiologic stress.

Is active sweating during heat acclimation required for improvements in peripheral sweat gland function

We investigated whether the eccrine sweat glands must actively produce sweat during heat acclimation if they are to adapt and increase their capacity to sweat. Eight volunteers received intradermal injections of BOTOX, to prevent neural stimulation and sweat production of the sweat glands during heat acclimation, and saline injections as a control in the contralateral forearm. Subjects performed 90 min of moderate-intensity exercise in the heat (35 degrees C, 40% relative humidity) on 10 consecutive days. Heat acclimation decreased end-exercise heart rate (156 +/- 22 vs. 138 +/- 17 beats/min; P = 0.0001) and rectal temperature (38.2 +/- 0.3 vs. 37.9 +/- 0.3 degrees C; P = 0.0003) and increased whole body sweat rate (0.70 +/- 0.29 vs. 1.06 +/- 0.50 l/h; P = 0.030). During heat acclimation, there was no measurable sweating in the BOTOX-treated forearm, but the control forearm sweat rate during exercise increased 40% over the 10 days (P = 0.040). Peripheral sweat gland function was assessed using pilocarpine iontophoresis before and after heat acclimation. Before heat acclimation, the pilocarpine-induced sweat rate of the control and BOTOX-injected forearms did not differ (0.65 +/- 0.20 vs. 0.66 +/- 0.22 mg x cm(-2) x min(-1)). However, following heat acclimation, the pilocarpine-induced sweat rate in the control arm increased 18% to 0.77 +/- 0.21 mg x cm(-2) x min(-1) (P = 0.021) but decreased 52% to 0.32 +/- 0.18 mg x cm(-2) x min(-1) (P < 0.001) in the BOTOX-treated arm. Using complete chemodenervation of the sweat glands, coupled with direct cholinergic stimulation via pilocarpine iontophoresis, we demonstrated that sweat glands must be active during heat acclimation if they are to adapt and increase their capacity to sweat.

Influence of fitness on susceptibility to noise-induced temporary threshold shift.

PURPOSE Two earlier reports indicated that cardiovascular fitness attenuates susceptibility to noise-induced temporary threshold shift (TTS) in hearing sensitivity; however, other parameters of fitness also may be related to this phenomenon. This study investigated the association of three different physical fitness indicators on TTS. METHODS Maximal aerobic power (VO2max), body composition. and recent activity history were determined in 33 normal-hearing females of various fitness levels. Audiometric thresholds were obtained at 2000, 3000, 4000, and 6000 Hz before and immediately after 10 min of exposure to 108-dB SPL narrow-band noise centered at 2000 Hz. RESULTS All postnoise measurements were significantly less than prenoise measurements (P < 0.0001) with the greatest TTS occurring at 3000 Hz. Similarly, the strongest Pearson-product correlations for VO2max, % fat, and recent activity history with TTS occurred at 3000 Hz (r = -0.68, 0.60, -0.59, respectively; P < 0.05). Canonical correlation analysis indicated a moderate correlation between physical fitness and TTS (Rc = 0.71: P < 0.01). Individually, VO2max, % fat, and recent activity history had correlations of -0.70, 0.62, and -0.63, respectively, to the TTS canonical variable. CONCLUSIONS From these results, we concluded that there is a moderate association of physical fitness and diminished temporary hearing loss experienced after noise exposure.

Effects of Sodium Bicarbonate on V̇o2 Kinetics during Heavy Exercise

PURPOSE Sodium bicarbonate was used to investigate the effect of blood pH on VO2 kinetics during heavy exercise. METHODS On separate days, 10 active subjects performed two 6-min cycling bouts (208 +/- 12 W) at 25 W above their ventilatory threshold. Each subject ingested 0.3 g x kg(-1) of sodium bicarbonate with approximately 1 L of water or water alone 1 h before exercise. VO2 kinetics were examined by means of a three-component mono-exponential model. RESULTS Bicarbonate ingestion caused a significant increase in the preexercise blood pH (7.512 +/- 0.009 vs 7.425 +/- 0.007; P < 0.001). In the bicarbonate trial, the time constant for the rapid component (27.9 +/- 3.5 s) was slower than the control trial (20.8 +/- 2.4 s; P = 0.017). The higher blood pH after bicarbonate ingestion would have diminished local blood flow and caused a leftward shift of the oxygen-hemoglobin dissociation curve both of which would slow oxygen delivery to working muscle. In addition, bicarbonate ingestion diminished the amplitude of the slow component 29% (463 +/- 43 vs 649 +/- 53 mL x min(-1); P = 0.040). The primary cause of the slow component during heavy exercise is fatigue of working fibers and an accompanying increase of motor unit recruitment. Elevated plasma bicarbonate concentration is reported to stimulate the efflux of H from muscle fibers and to increase intramuscular pH. CONCLUSIONS The slower time constant during the rapid component suggested that oxygen delivery is a limiting factor of VO2 kinetics during the onset of heavy exercise. Also, these results imply that bicarbonate ingestion diminished fatigue in working fibers during the slow component.

Effect of acute normobaric hypoxia on peripheral sweat rate.

Peripheral sweat rate was measured to determine if acute normobaric hypoxia exerted a local inhibition on sweat gland function. It was hypothesized that peripheral sweat rate would be reduced during hypoxia, following cholinergic stimulation. Nineteen subjects (24 +/- 3 yr; 177 +/- 9 cm; 75.5 +/- 20.1 kg), 8 females and 11 males, were tested once during normobaric hypoxia, simulating an altitude of approximately 3050 m (P(O2) = 13.9%; P(B) approximately 730 mmHg), and once at sea level (200 m; P(O2) = 20.9%; P(B) approximately 730 mmHg). While seated at rest, a approximately 7-cm(2) area of the anterior forearm was stimulated using pilocarpine iontophoresis to produce localized sweating at the site. Following stimulation, sweat was collected from the area for 15 min using a Macroduct Sweat Collection System. One-way repeated measures ANOVA indicated a significantly lower sweat rate during normobaric hypoxia (4.6 +/- 2.6 g x m(-2) x min(-1)) compared to sea level (5.5 +/- 3.0 g x m(-2) x min(-1); p = 0.006). Because sweating was initiated directly at the sweat gland, thus bypassing central nervous system input, changes in sweat rate were likely due to peripheral alterations. Although these peripheral mechanisms warrant further investigation, the results of this study suggest a direct hypoxic influence on sweat gland function as evidenced by a decrease in sweat rate.

Evaluation of the ventilatory effects of the prone maximum restraint (PMR) position on obese human subjects

UNLABELLED The study sought to determine the physiologic effects of the prone maximum restraint (PMR) position in obese subjects after intense exercise. We designed an experimental, randomized, cross-over trial in human subjects conducted at a university exercise physiology laboratory. Ten otherwise healthy, obese (BMI>30) subjects performed a period of heavy exertion on a cycling ergometer to 85% of maximum heart rate, and then were placed in one of three positions in random order for 15min: (1) seated with hands behind the back, (2) prone with arms to the sides, (3) PMR position. While in each position, mean arterial blood pressure (MAP), heart rate (HR), minute ventilation (V˙E), oxygen saturation (SaO2), and end tidal CO2(etCO2) were measured every 5min. There were no significant differences identified between the three positions in MAP, HR, V˙E, or O2sat at any time period. There was a slight increase in heart rate at 15min in the PMR position over the prone position (95 vs. 87). There was a decrease in end tidal CO2 at 15min in the PMR over the prone position (32mmHg vs. 35mmHg). In addition, there was no evidence of hypoxia or hypoventilation during any of the monitored 15min position periods. CONCLUSION In this small study of obese subjects, there were no clinically significant differences in the cardiovascular and respiratory measures comparing seated, prone, and PMR position following exertion.

Evaluation of the Ventilatory Effects of a Restraint Chair on Human Subjects

BACKGROUND Combative individuals often require physical restraint in the prehospital and law enforcement setting. Specialized restraint chairs have been utilized for this purpose in the latter case, but concern has arisen that restrained individuals are at risk for ventilatory compromise and asphyxiation. OBJECTIVE We sought to determine if placement in a restraint chair results in alterations of respiratory or ventilatory function. METHODS We conducted a randomized, cross-over, controlled experimental trial in 10 healthy human volunteers performed at a university exercise physiology laboratory. After exercise on a cycle ergometer to 85% of the age-predicted maximal heart rate, subjects were randomized to either a sitting position or restraint chair with arms, legs, and chest secured using standard law enforcement protocol. Subjects remained in each position for 30 min, during which pulmonary function testing of maximal voluntary ventilation (MVV) was performed at 11 and 30 min. Arterial oxygen saturation (O(2)sat) and end-tidal PCO(2) levels (PETCO(2)) were monitored continuously. Subjects repeated the experimental trial in the alternate position after a 45-min rest period. Measures between restraint and sitting positions were compared using a paired t-test at each time measurement. RESULTS There was no evidence of hypoxemia. Mean PETCO(2) levels were not statistically different between the two groups at any time (p > 0.05), and there was no evidence of hypercapnia. CONCLUSION In healthy subjects, placement in a restraint chair resulted in a small decrease in MVV, but did not result in any changes in O(2)sat or PETCO(2).

Expired air temperature during steady-state running

While some metabolic measurement systems measure expiratory temperature to standardize gas volumes, other systems use only an estimate. This study investigated the effect of prolonged exercise on expiratory temperature near the pneumotachometer to provide a basis for its estimation when actual measurement is unavailable. Seven active females each performed two 45-min treadmill runs at identical speeds (64.5% +/- 11.8% of VO2max) in which the pneumotachometer heater control was either set to 37 degrees C or turned off. Expired air temperatures were monitored with thermocouples at the nonrebreathing valve (VAL) and 1 cm upstream (UPS) and downstream (DNS) from the pneumotachometer screens. There were no temperature differences over time for any of the conditions, and there were no differences in the VAL or UPS temperatures between the heated and unheated conditions. DNS temperature was higher during the heated condition at all time periods (P < 0.01). Mean DNS temperatures for the heated and unheated condition were 30.2 +/- 1.0 degree C and 27.9 +/- 1.1 degrees C, respectively. We conclude that expired air temperatures near the pneumotachometer remain stable during extended steady-state exercise regardless of whether the pneumotachometer is heated or not.