Thermoregulatory responses to low-intensity prolonged swimming in water at various temperatures and treadmill walking on land

The purpose of the present study was to examine the effect of water temperature on the human body during low-intensity prolonged swimming. Six male college swimmers participated in this study. The experiments consisted of breast stroke swimming for 120 minutes in 23 degrees C, 28 degrees C and 33 degrees C water at a constant speed of 0.4 m.sec-1 in a swimming flume. The same subjects walked on a treadmill at a rate of approximately 50% of maximal oxygen uptake (VO2max) at the same relative intensity as the three swimming trials. Rectal temperature (Tre) in 33 degrees C water was unchanged during swimming for 120 minutes. Tre during treadmill walking increased significantly compared to the three different swimming trials. Tre, mean skin temperature (Tsk) and mean body temperature (Tb) in 23 degrees C and 28 degrees C water decreased significantly more than in both the 33 degrees C water and walking on land. VO2 during swimming in 23 degrees C water increased more than during swimming in the 28 degrees C and 33 degrees C trials; however, there were no significant differences in VO2 between the 23 degrees C swimming trial and treadmill walking. Heart rate (HR) during treadmill walking on land increased significantly compared with HR during the three swimming trials. Plasma adrenaline concentration at the end of the treadmill walking was higher than that at the end of each of the three swimming trials. Noradrenaline concentrations at the end of swimming in the 23 degrees C water and treadmill walking were higher than those during the other two swimming trials. Blood lactate concentration during swimming in 23 degrees C water was higher than that during the other two swimming trials and walking on land. These results suggest that the balance of heat loss and heat production is maintained in the warm water temperature. Therefore, a relatively warm water temperature may be desirable when prolonged swimming or other water exercise is performed at low intensity.     

Cardiorespiratory response to low-intensity walking in water and on land in elderly women.

The purpose of the present study was to determine whether or not the exercise intensity of water-walking for elderly women could be accurately prescribed by heart rate data obtained during treadmill exercise on land. Six healthy female volunteers, with a mean age of 62.2 +/- 4.2 years, took part in this study. Walking on land was performed on a treadmill. Each subject completed three consecutive 4-minute walks at a progressively increasing velocity (40, 60 and 80 m.min-1), with a 1-minute rest after both the first and second walks. The room temperature and relative humidity were 24.5 +/- 0.2 degrees C and 54.8 +/- 4.0%, respectively. Walking in water was performed in a Flowmill, which is a treadmill positioned at the base of a water flume. Each subject completed three consecutive 4-minute walks at a progressively increasing belt and water-flow velocity (20, 30 and 40 m.min-1), with a 1-minute rest after both the first and second walks. The water depth was at the level of the xiphoid process of each subject. The water temperature was 30.7 +/- 0.1 degrees C. The exercise intensity at the highest workrate was equivalent to 44.2 +/- 10.3% of the heart rate reserve (HRR) during water-walking and 38.4 +/- 4.7% of the HRR during land-walking. There was a highly significant linear relationship between heart rate (HR) and oxygen uptake (VO2) during both water-walking and land-walking. The relationship between HR and VO2 in both exercise modes was similar. Thus, the relationship of HR to VO2 derived from a treadmill-graded walking test on land may be used to prescribe exercise intensity for water-walking in thermoneutral water.     

Use of perceived effort ratings to control exercise intensity in young healthy adults

The purpose of this study was to evaluate the use of the rating of perceived exertion (RPE) as a means of regulating the intensity of exercise during running. The subjects were healthy, relatively fit young adults (16 men and 12 women). Estimates of effort were recorded using the Borg 6-20 Scale whilst the maximal oxygen uptake of the subjects was measured as they ran on an electrically driven treadmill. In a further session, the same subjects were requested to run on the treadmill at constant exercise intensity based on their interpretation of levels 9, 13 and 17 of the Borg Scale. They regulated their running speed and the treadmill gradient but had no knowledge of performance from the equipment display panel. A linear regression analysis was carried out to examine the relationship between heart rate, perceived exertion and relative metabolic demand. This revealed that the rating of perceived exertion was at least as good a predictor of exercise intensity as heart rate in both the graded exercise test and effort production test. The results support the view that RPE may be used to predict relative metabolic demand, especially at higher workloads and could be a useful medium for controlling intensity of effort during vigorous exercise in such subjects.     

The physiological effects of caffeine in women during treadmill walking

Although the effects of caffeine ingestion on athletic performance in men have been studied extensively, there is limited previous research examining caffeine's effects on women of average fitness levels participating in common modes of physical activity. The purpose of this study was to determine the effect of 2 levels of caffeine dosage on the metabolic and cardiorespiratory responses to treadmill walking in women. Subjects were 20 women (19-28 years of age) of average fitness, not habituated to caffeine. Each subject was assigned randomly a 3-mg x kg(-1) dose of caffeine, 6-mg x kg(-1) dose of caffeine, and placebo for 3 trials of moderate steady-state treadmill walking at 94 m x min(-1) (3.5 mph). Steady-state rating of perceived exertion (RPE), heart rate (HR), respiratory exchange ratio (RER), weight-relative VO2, %VO2max reserve (%VO2R), and rate of energy expenditure (REE) were measured during each trial. Repeated measures analysis of variance revealed that a 6-mg x kg(-1), but not a 3-mg x kg(-1) dose of caffeine increased VO2 (p = 0.04), REE (p = 0.03), and %VO2R (p = 0.03), when compared to the placebo. Caffeine had no effect on RPE, HR, or RER. No significant differences were observed between the placebo trials and the 3-mg x kg(-1) dose trials. Although a 6-mg x kg(-1) dose of caffeine significantly increased REE during exercise, the observed increase (approximately 0.23 kcal x min(-1)) would not noticeably affect weight loss. Because caffeine had no effect on RPE, it would not be prudent for a trainer to recommend caffeine in order to increase a woman's energy expenditure or to decrease perception of effort during mild exercise. These data also demonstrate that caffeine intake should not interfere with monitoring walking intensity by tracking exercise heart rate in women.     

Effect of submaximal exercise at low temperatures on pulmonary function in healthy young men

In order to understand more fully the effect on pulmonary function of whole body exposure to cold during submaximal exercise, we measured pulmonary function indices in ten healthy male students and ten healthy male forestry workers of similar age following submaximal treadmill walking at different temperatures in a climatic chamber. After measuring the maximal aerobic capacity with a cycle ergometer test, the subjects had to walk on four separate occasions in the climatic chamber at an intensity of 70%-75% of their individual maximal heart rate; the first at normal room temperature and then randomly, either at 0 degrees C or at -20 degrees C, and vice versa. The duration of each walk was 8 min. Finally, each subject had to walk in the chamber at -20 degrees C for 17 min. Flow volume spirometry was performed at room temperature 1, 5, 10, and 20 min after exercise and the values were compared to baseline values taken prior to the last walking test. There were only minor changes in pulmonary function indices following exercise at different temperatures. Only one student showed a reduction of over 15% in peak expiratory flow rate after an 8-min walk at -20 degrees C. It seems that submaximal exercise of short duration, even at a temperature as low as -20 degrees C, does not impair pulmonary function in healthy young men.     

Effects of metabolic rate on thermal responses at different air velocities in -10 degrees C

The effects of exercise intensity on thermoregulatory responses in cold (-10 degrees C) in a 0.2 (still air, NoWi), 1.0 (Wi1), and 5.0 (Wi5) m x s(-1) wind were studied. Eight young and healthy men, preconditioned in thermoneutral (+20 degrees C) environment for 60 min, walked for 60 min on the treadmill at 2.8 km/h with different combinations of wind and exercise intensity. Exercise level was adjusted by changing the inclination of the treadmill between 0 degrees (lower exercise intensity, metabolic rate 124 W x m(-2), LE) and 6 degrees (higher exercise intensity, metabolic rate 195 W x m(-2), HE). Due to exercise increased heat production and circulatory adjustments, the rectal temperature (T(re)), mean skin temperature (Tsk) and mean body temperature (Tb) were significantly higher at the end of HE in comparison to LE in NoWi and Wi1, and T(re) and Tb also in Wi5. Tsk and Tb were significantly decreased by 5.0 m x s(-1) wind in comparison to NoWi and Wi1. The higher exercise intensity was intense enough to diminish peripheral vasoconstriction and consequently the finger skin temperature was significantly higher at the end of HE in comparison to LE in NoWi and Wi1. Mean heat flux from the skin was unaffected by the exercise intensity. At LE oxygen consumption (VO2) was significantly higher in Wi5 than NoWi and Wi1. Heart rate was unaffected by the wind speed. The results suggest that, with studied exercise intensities, produced without changes in walking speed, the metabolic rate is not so important that it should be taken into consideration in the calculation of wind chill index.     

Crossmodal session rating of perceived exertion response at low and moderate intensities

Session rating of perceived exertion (SRPE) permits global effort estimations after an exercise bout and has shown promise for evaluating training load. However, factors mediating SRPE are not well understood. The purpose of this study was to compare SRPE between cycling and treadmill exercise at low and moderate intensities. In a counterbalanced order, male subjects (n = 7) completed a VO2max trial on a cycle ergometer and a motor-driven treadmill. Then, participants completed trials at 50 and 75% mode-specific VO2max on a cycle ergometer (BK75, BK50) and a treadmill (TM75, TM50) to achieve ～ 400-kcal energy expenditure per trial. Acute RPE (i.e., during exercise) at 5 minutes, midway, and test termination were recorded with SRPE (20-minutes postexercise) expressed as overall (SRPEO), legs (SRPEL), and breathing also recorded were heart rate (HR) and change in rectal temperature (ΔTrec). Significance was accepted at p ≤ 0.05. Repeated-measures analysis of variance revealed significantly greater SRPE for higher intensities within each mode. Crossmodal comparisons also show a higher SRPE at moderate (75% VO2max) intensities [SRPEO] = BK75: 7.6 ± 1.0, TM75: 6.9 ± 1.3) vs. lower (50% VO2max) intensities (BK50: 4.6 ± 1.4, TM50: 4.6 ± 1.1). Within modes, SRPE corresponded well with ΔTrec and HR. Acute RPE was linked with intensity and drifted upward across time. Results indicated that overall and differentiated SRPEs are magnified with exercise intensity with the corresponding disruption in internal environment potentially mediating subjective responses. From a practical application standpoint, SRPE provides a subjective assessment for immediate evaluation of daily training. Results indicate that, when using SRPE to monitor training, consideration should be given to responses across differing exercise modes.     

Concurrent validity of an OMNI rating of perceived exertion scale for bench stepping exercise

To develop and validate a modified OMNI rating of perceived exertion (RPE) scale for use during bench stepping exercise (OMNI-BS). Thirty women (age: 19.8 ± 1.8 years) undertook 2 experimental trials, separated by 7 days. Concurrent validity was established by examining the relation between physiological criterion variables, oxygen consumption (VO2), and heart rate (HR), with the concurrent variable, RPE from OMNI-BS, during 2 trials in which the intensity increased linearly (test 1) and intermittently (test 2). The first test consisted of 3-minute stages. Subjects stepped up and down on the bench at 120 b·min(-1). The test was terminated owing to subject fatigue. Exercise intensity increased as bench height increased every 3 minutes. The second test consisted of three 3-minute exercise bouts that reproduced exercise stage 1 (low intensity), stage 3 (moderate intensity), and stage 5 (high intensity) performed in the first test. The order of these 3 exercise bouts was counterbalanced. Intraclass correlation analysis from experimental trials indicated a strong positive association between RPE and VO2 (r = 0.96 and r = 0.95) and HR (r = 0.95 and r = 0.95). Concurrent validity for the OMNI-BS RPE scale was established for women performing bench stepping exercise.     

Monitoring exercise intensity during resistance training using the session RPE scale

This study investigated the reliability of the session rating of perceived exertion (RPE) scale to quantify exercise intensity during high-intensity (H), moderate-intensity (M), and low-intensity (L) resistance training. Nine men (24.7 +/- 3.8 years) and 10 women (22.1 +/- 2.6 years) performed each intensity twice. Each protocol consisted of 5 exercises: back squat, bench press, overhead press, biceps curl, and triceps pushdown. The H consisted of 1 set of 4-5 repetitions at 90% of the subject's 1 repetition maximum (1RM). The M consisted of 1 set of 10 repetitions at 70% 1RM, and the L consisted of 1 set of 15 repetitions at 50% 1RM. RPE was measured following the completion of each set and 30 minutes postexercise (session RPE). Session RPE was higher for the H than M and L exercise bouts (p < or = 0.05). Performing fewer repetitions at a higher intensity was perceived to be more difficult than performing more repetitions at a lower intensity. The intraclass correlation coefficient for the session RPE was 0.88. The session RPE is a reliable method to quantify various intensities of resistance training.     

Comparison between Nintendo Wii Fit aerobics and traditional aerobic exercise in sedentary young adults

Exergaming is becoming a popular recreational activity for young adults. The purpose was to compare the physiologic and psychological responses of college students playing Nintendo Wii Fit, an active video game console, vs. an equal duration of moderate-intensity brisk walking. Twenty-one healthy sedentary college-age students (mean age 23.2 ± 1.8 years) participated in a randomized, double cross-over study, which compared physiologic and psychological responses to 30 minutes of brisk walking exercise on a treadmill vs. 30 minutes playing Nintendo Wii Fit "Free Run" program. Physiologic parameters measured included heart rate, rate pressure product, respiratory rate, and rating of perceived exertion. Participants' positive well-being, psychological distress, and level of fatigue associated with each exercise modality were quantified using the Subjective Exercise Experience Scale. The mean maximum heart rate (HRmax) achieved when exercising with Wii Fit (142.4 ± 20.5 b·min(-1)) was significantly greater (p = 0.001) compared with exercising on the treadmill (123.2 ± 13.7 b·min(-1)). Rate pressure product was also significantly greater (p = 0.001) during exercise on the Wii Fit. Participants' rating of perceived exertion when playing Wii Fit (12.7 ± 3.0) was significantly greater (p = 0.014) when compared with brisk walking on the treadmill (10.1 ± 3.3). However, psychologically when playing Wii Fit, participants' positive well-being decreased significantly (p = 0.018) from preexercise to postexercise when compared with exercising on the treadmill. College students have the potential to surpass exercise intensities achieved when performing a conventional standard for moderate-intensity exercise when playing Nintendo Wii Fit "Free Run" with a self-selected intensity. We concluded that Nintendo Wii Fit "Free Run" may act as an alternative to traditional moderate-intensity aerobic exercise in fulfilling the American College of Sports Medicine requirements for physical activity.     

Electromyographic analysis of walking in water in healthy humans

This study was designed to describe and clarify muscle activities which occur while walking in water. Surface electromyography (EMG) was used to evaluate muscle activities in six healthy subjects (mean age, 23.3 +/- 1.4 years) while they walked on a treadmill in water (with or without a water current) immersed to the level of the xiphoid process, and while they walked on a treadmill on dry land. The trials in water utilized the Flowmill which has a treadmill at the base of a water flume. Integrated EMG analysis was conducted for the quantification of muscle activities. In order to calculate the %MVC, the measurement of maximal voluntary contraction (MVC) of each muscle was made before the gait analysis, thus facilitating a comparison of muscle activities while walking in water with those on dry land. The %MVCs obtained from each of the tested muscles while walking in water, both with and without a water current, were all found to be lower than those obtained while walking on dry land at a level of heart rate response similar to that used when walking on dry land. Furthermore, the %MVCs while walking in water with a water current tended to be greater when compared to those while walking in water without a water current. In conclusion, the present study demonstrated that muscle activities while walking in water were significantly decreased when compared to muscle activities while walking on dry land, that muscle activities while walking in water tended to be greater with a water current than without, and that the magnitude of the muscle activity in water was relatively small in healthy humans. This information is important to design water-based exercise programs that can be safely applied for rehabilitative and recreational purposes.     

A comparison of the physiological exercise intensity differences between shod and barefoot submaximal deep-water running at the same cadence

The purpose of this investigation was to identify whether physiological exercise intensity differed with the use of aquatic training shoes (ATS) during deep-water running (DWR) compared to using a barefoot condition. Eight male intercollegiate (National Collegiate Athletic Association Division III [NCAA III]) varsity distance runners were videotaped from the right sagittal view while running on a treadmill (TR) and while barefoot in deep water at 60-70% of their TR VO2max for 30 minutes. Based on the stride rate of the barefoot DWR trial, a subsequent 30-minute session was completed while wearing ATS. Variables of interest were energy expenditure, oxygen consumption (VO2), heart rate, respiratory exchange ratio (RER), and rating of perceived exertion (RPE). Multivariate omnibus tests revealed statistically significant differences for energy expenditure (p < 0.011), VO2 (p < 0.001), RPE (p < 0.001), and RER (p < 0.002). The post hoc pairwise comparisons revealed significant differences between barefoot and shod DWR conditions for energy expenditure (p < 0.005) and VO2 (p < 0.002), representing a 9 and 7.6% increase in exercise intensity demand while running shod vs. barefoot. These comparisons also revealed significantly higher RPE and RER values while DWR than those found in TR. Wearing the ATS may be recommended as a method of statistically significantly increasing the exercise intensity while running in deep water as compared to not wearing a shoe. Shod compared to TR yields very small differences, which indicates that the shoes may help better match land-based running exercise intensities.     

Hypohydration adversely affects lactate threshold in endurance athletes

The purpose of this investigation was to observe the effect of hypohydration (-4% body mass) on lactate threshold (LAT) in 14 collegiate athletes (8 men and 6 women; age, 20.9 +/- 0.5 years; height, 171.1 +/- 2.4 cm; weight, 64.8 +/- 2.3 kg; V(O)2 max, 62.8 +/- 1.9 ml x kg(-1) x min(-1); percentage of fat, 11.4 +/- 1.5%). Subjects performed 2 randomized, discontinuous treadmill bouts at a dry bulb temperature (T(db)) of 22 degrees C to volitional exhaustion in 2 states of hydration, euhydrated and hypohydrated. The hypohydrated condition was achieved in a thermally neutral environment (T(db), 22 degrees C; humidity, 45%), with exercise conducted at a moderate intensity as defined by rating of perceived exertion (RPE, approximately 12) 12-16 hours before testing. On average, subjects decreased 3.9% of their body mass before the hypohydration test. Blood lactate, hematocrit, V(O)2, minute ventilation (VE), R value, heart rate (HR), and RPE were measured during each 4-minute stage of testing. In the hypohydrated condition, LAT occurred significantly earlier during exercise and at a lower absolute V(O)2, VE, respiratory exchange ratio, RPE, and blood lactate concentration. Also, the blood lactate concentration was significantly lower in the hypohydrated condition (6.7 +/- 0.8 mmol) compared with the euhydrated condition (10.2 +/- 0.9 mmol) at peak exercise. There were no differences in HR or percentage of maximum HR at LAT nor did plots of V(CO2):V(O)2 reveal differences in bicarbonate buffering during exercise between the 2 conditions. From these results, we speculate that hypohydration did not significantly alter cardiovascular function or buffering capacity but did cause LAT to occur at a lower absolute exercise intensity.     

Stress hormones, effort sense, and perceptions of stress during incremental exercise: an exploratory investigation

Exercise elicits intensity-dependent increases in epinephrine (Epi), norepinephrine (NE), cortisol (CORT), and lactate (Lac), whereas at rest the hormonal responses to mental stress include increases in Epi, NE, and CORT, but not Lac. Additionally, elevations in CORT at rest are associated with negative affect. Finally, as exercise intensity increases, perceptions of effort (RPE) increase and affect becomes more negative. The purpose of this study was to examine the responses of Epi, NE, CORT, Lac, RPE, and affect during incremental increases in exercise to maximum. Seven highly-trained male runners completed a discontinuous treadmill protocol that included 10 minutes at 60%, 10 minutes at 75%, 5 minutes at 90%, and 2 minutes at 100% of VO2max. Blood samples were collected through an intravenous catheter before, during, and following exercise during the experimental condition, and during a time-matched control condition. RPE and affect were assessed just prior to each blood draw. The Epi, NE, CORT, and Lac displayed the expected incremental increases, however affect became more negative at higher exercise intensities, and RPE increased as exercise intensity increased. Data suggest that CORT follows the same pattern of response to graded exercise as affect. Since perceptual and affective responses to exercise are associated with motivation, these documented negative affective shifts during exercise should be considered in order to develop strategies that lead to enhanced exercise adherence and performance.     

Quantitation of resistance training using the session rating of perceived exertion method

The purpose of this study was to apply the session rating of perceived exertion (RPE) method, which is known to work with aerobic training, to resistance training. Ten men (26.1 +/- 10.2 years) and 10 women (22.2 +/- 1.8 years), habituated to both aerobic and resistance training, performed 3 x 30 minutes aerobic training bouts on the cycle ergometer at intensities of 56%, 71%, and 83% Vo(2) peak and then rated the global intensity using the session RPE technique (e.g., 0-10) 30 minutes after the end of the session. They also performed 3 x 30 minutes resistance exercise bouts with 2 sets of 6 exercises at 50% (15 repetitions), 70% (10 repetitions), and 90% (4 repetitions) of 1 repetition maximum (1RM). After each set the exercisers rated the intensity of that exercise using the RPE scale. Thirty minutes after the end of the bout they rated the intensity of the whole session and of only the lifting components of the session, using the session RPE method. The rated intensity of exercise increased with the %Vo(2) peak and the %1RM. There was a general correspondence between the relative intensity (%Vo(2) peak and % 1RM) and the session RPE. Between different types of resistance exercise at the same relative intensity, the average RPE after each lift varied widely. The resistance training session RPE increased as the intensity increased despite a decrease in the total work performed (p < 0.05). Mean RPE and session RPE-lifting only also grew with increased intensity (p < 0.05). In many cases, the mean RPE, session RPE, and session RPE- lifting only measurements were different at given exercise intensities (p < 0.05). The session RPE appears to be a viable method for quantitating the intensity of resistance training, generally comparable to aerobic training. However, the session RPE may meaningfully underestimate the average intensity rated immediately after each set.     

Effect of exercise intensity on the postexercise sweating threshold.

The hypothesis that the magnitude of the postexercise onset threshold for sweating is increased by the intensity of exercise was tested in eight subjects. Esophageal temperature was monitored as an index of core temperature while sweat rate was measured by using a ventilated capsule placed on the upper back. Subjects remained seated resting for 15 min (no exercise) or performed 15 min of treadmill running at either 55, 70, or 85% of peak oxygen consumption (V(o2 peak)) followed by a 20-min seated recovery. Subjects then donned a liquid-conditioned suit used to regulate mean skin temperature. The suit was first perfused with 20 degrees C water to control and stabilize skin and core temperature before whole body heating. Subsequently, the skin was heated ( approximately 4.0 degrees C/h) until sweating occurred. Exercise resulted in an increase in the onset threshold for sweating of 0.11 +/- 0.02, 0.23 +/- 0.01, and 0.33 +/- 0.02 degrees C above that measured for the no-exercise resting values (P < 0.05) for the 55, 70, and 85% of V(o2 peak) exercise conditions, respectively. We did note that there was a greater postexercise hypotension as a function of exercise intensity as measured at the end of the 20-min exercise recovery. Thus it is plausible that the increase in postexercise threshold may be related to postexercise hypotension. It is concluded that the sweating response during upright recovery is significantly modified by exercise intensity and may likely be influenced by the nonthermal baroreceptor reflex adjustments postexercise.     

Effects of saddle height on economy in cycling

Research has demonstrated that properly adjusting saddle height is important for both performance and injury prevention during cycling. Peer-reviewed literature recommends the use of a 25 degrees to 35 degrees knee angle for injury prevention and 109% of inseam for optimal performance. Previous research has established that these 2 methods do not produce similar saddle heights. Previous research has also compared anaerobic power among a 25 degrees knee angle, a 35 degrees knee angle, and 109% of inseam and found an increase in anaerobic power at a 25 degrees knee angle. While anaerobic power production has been compared between these 2 methods, aerobic power and economy have not been. The purpose of this study was to determine the difference in economy between these 2 methods of adjusting saddle height. Fifteen subjects, consisting of 5 cyclists (all men) and 10 noncyclists (2 men and 8 women), participated in this study. A graded exercise protocol was utilized in order to determine intensity for the remaining trials. On the last 3 trials, subjects rode for 15 minutes at the resistance at which they reached 70% of Vo2max on a cycle ergometer. Vo2, heart rate (HR), and rating of perceived exertion (RPE) were compared to detect differences in economy between saddle heights. No significant differences were noted in HR or RPE. Vo2 was found to be significantly lower at a saddle height set with a 25 degrees knee angle when compared to a 35 degrees knee angle and 109% of inseam. Findings from this study support the use of a 25 degrees knee angle for both performance and injury prevention.