Incremental Treadmill Walking Research Articles

Development and validation of a 1-km cardio-trekking test to estimate cardiorespiratory fitness in healthy adults

Maximum oxygen uptake (V̇O2max), the gold standard measure of cardiorespiratory fitness (CRF), supports cardiovascular risk assessment and is mainly assessed during maximal spiroergometry. However, for field use, submaximal exercise tests might be appropriate and feasible. There have been no studies attempting a submaximal test protocol involving uphill hiking. This study aimed to develop and validate a 1-km cardio-trekking test (CTT) controlled by heart rate monitoring and Borg’s 6–20 rating of perceived exertion (RPE) scale to predict V̇O2max outdoors. Healthy participants performed a maximal incremental treadmill walking laboratory test and a submaximal 1-km CTT on mountain trails in Austria and Germany, and V̇O2max was assessed with a portable spirometry device. Borg’s RPE scale was used to control the exercise intensity of the CTT. All subjects wore a chest strap to measure heart rate (HR). A total of 134 participants (median age: 56.0 years [IQR: 51.8–63.0], 43.3 % males) completed both testing protocols. The prediction model is based on age, gender, smoking status, weight, mean HR, altitude difference, duration, and the interaction between age and duration (R2 = 0.65, adj. R2 = 0.63). Leave-one-out cross-validation revealed small shrinkage in predictive accuracy (R2 = 0.59) compared to the original model. Submaximal exercise testing using uphill hiking allows for practical estimation of V̇O2max in healthy adults. This method may allow people to engage in physical activity while monitoring their CRF to avert unnecessary cardiovascular events.

Effects Of Modern Military Footwear On The Metabolic Demands Of Walking

Quantifying the metabolic costs of carrying or wearing various military uniform components is essential for accurate assessment of the metabolic cost of warfighters performing military tasks under scenarios and environmental conditions. PURPOSE: Evaluate the metabolic demand of walking at incremental speeds in a controlled laboratory environment while wearing military-issued combat boots compared to athletic sneakers. METHODS: In this randomized, cross-over study, nineteen active military-age men (age, 24 ± 5 years; height, 177 ± 6 cm; body mass, 80 ± 13 kg) performed an incremental treadmill walking test in combat boots and athletic sneakers on separate visits. Treadmill speed started at 4.18 km/h for 3 min, then increased by 0.23 km/h every 2 min. Tests were terminated when volunteers either completed the highest treadmill speed (7.08 km/h), reached volitional fatigue, or exceeded a respiratory exchange ratio of 1.0. Volunteers exhaled into a laboratory metabolic cart that measured expired gases. Metabolic demand was quantified as the average oxygen uptake (V̇O2) over the final minute of each walking speed. RESULTS: Across all speeds, walking in combat boots resulted in significantly higher V̇O2 than walking in athletic sneakers (0.63 ± 1.05 mL·kg-1·min-1; p = 0.01). Regression analysis determined a V̇O2 difference between footwear of 0.31 mL·kg-1·min-1 at 4.18 km/h that increased by 0.22 mL·kg-1·min-1 with each 1 km/h increase (R2, 0.68). Regressing walking V̇O2 when wearing combat boots on walking V̇O2 while wearing athletic sneakers revealed both a positive offset and slope (Trendline, V̇O2boots = 0.04 + 1.04·V̇O2sneakers; R2, 0.97). CONCLUSIONS: The metabolic demand of walking in military combat boots is greater and more pronounced at increased walking speeds than when wearing common athletic sneakers. The views expressed in this abstract are those of the authors and do not reflect the official policy of the Department of Army, Department of Defense, or the U.S. Government.

Impact of high-heeled and sport shoes on multi-joint external load profile during walking.

Previous studies have analysed the effect of wearing high-heeled shoes (HHS) on gait analysis, balance and its relation to health. However, further research is needed to study its effect on the difference of chain reactions in the transfer of body impacts from the lower to the upper limbs. The aims of the present research were: (a) to compare the effects of wearing HHS on impacts across body joints during walking with sport shoes (SS) as a reference, and (b) to examine such effects at different speeds. Seven well-trained women completed this study. Incremental treadmill walking test were performed with two different footwear: SS and HHS. Inertial devices were used to quantify the chain reactions at selected anatomical lower limbs and trunk locations. Statistical analysis included the Wilcoxon test with ranges and Cohen's d effect size with percentage of differences. The highest values were found at the heel in both footwear and in both legs (SS: right =0.76 ± 0.27, left = 0.79 ± 0.27; HHS: right = 1.07 ± 0.38, left = 1.11 ± 0.41), while the lowest values were registered at lower and upper back. Furthermore, significant differences were found with the HHS load being higher at all locations (p< 0.05; %=𝑑𝑖𝑓𝑓 12.20-36.36%), influenced by the walking speed. In addition, a strong influence of footwear in the change of the laterality profile was found (p< 0.05). These findings suggest that the use of HHS increase the load on the lower limb and the trunk. Until reaching 5 km/h during walking, no significant differences were found between wearing HHS or SS in accelerometer load, producing exponential differences from this speed. The great between-subject variability implies that within-subject analysis is recommended, as it is more related to real clinical practice.

The effect of participating in MedEx Wellness, a community-based chronic disease exercise rehabilitation programme, on physical, clinical and psychological health: A study protocol for a cohort trial

BackgroundCommunity-based exercise rehabilitation programmes for chronic disease are an effective alternative to traditional hospital-based programmes. MedEx Wellness is a novel community-based exercise rehabilitation programme that integrates a range of chronic diseases. The aim of this trial was to investigate the effect of participating in MedEx Wellness on physical, clinical and psychological health. MethodsA prospective cohort study was conducted. Participants were recruited at induction to the MedEx Wellness programme following referral from healthcare professionals. Participants underwent a baseline assessment before commencing the exercise programme and repeat assessments at 3, 6 and 12 months. The primary outcome was cardiorespiratory fitness (6 minute- time trial) at 12 months. Secondary outcomes included health-related quality of life (EuroQoL-5D, Satisfaction with Life Scale, Warwick Edinburgh Mental Wellbeing Scale, Patient Health Questionnaire8, Functional Assessment of Cancer Therapy Questionnaire), free living activity behavior (accelerometer) and healthcare utilization (recall questionnaire). Tertiary outcomes included blood pressure (24 h), biomarkers (lipids, glucose and C-reactive protein), other components of physical fitness, including strength (handgrip test, sit-to-stand test), flexibility (sit-and-reach test), body composition (body mass index and waist-to-hip ratio), and falls risk (timed up and go test), and claudication time (incremental treadmill walking test), cognitive function, including attention (Attention Network Task), memory (Luck & Vogel Visual Working Memory Task) and cognitive reserve. Exploratory outcomes included psychosocial determinants of physical activity (self-efficacy, social support, intentions). DiscussionThis trial will evaluate whether participation in the MedEx Wellness programme has positive effects on physical, clinical and psychological health in individuals with a range of chronic diseases. Trial registrationISRCTN Registry ISRCTN10351412.

Changes in substrate utilization rates during 40min of walking within the Fatmax range.

The aim of this study was to evaluate changes in fat oxidation rate during 40min of continuous exercise and identify the intensity at the highest fat oxidation rate (Fatmax). A total of 14 sedentary males with age, body height, weight, and BMI averages of 29.3 ± 0.7 years, 178.3 ± 1.7cm, 81.1 ± 3.9kg, and 25.4 ± 0.9kg/m2, respectively, were included in the study. Fatmax was determined using an indirect calorimeter with an incremental treadmill walking test at least after 12h of fasting. On a separate day, at least after 12h of fasting, the participants walked for 40min within their predetermined individual Fatmax heart rate and speed ranges. The initial fat oxidation rate was not sustained within the first 16min of exercise and was reduced; however, carbohydrate oxidation reached a stable level after nearly 10min. In sedentary individuals, during low-intensity physical activity, fat oxidation rates may not be sustainable as expected from Fatmax testing. Therefore, when exercise is prescribed, one should consider that the fat oxidation rate might decrease in sedentary overweight individuals.

Walking performance in adolescents and young adults with Down syndrome: the role of obesity and sleep problems.

High prevalence of obesity and features of obstructive sleep apnea (OSA) are major health issues in individuals with Down syndrome (DS), and both may also affect adversely on their daily activities. Further, lower levels of physical work capacity (PWC) have been reported in this population compared to their peers with intellectual disabilities. However, no study examines the relationships between obesity and sleep problems with PWC in individuals with DS. Thus, this study investigated the influence of body mass index (BMI) and different types of sleep problems on PWC in adolescents and young adults with DS (14-31years). The incremental treadmill walking trial was used to assess PWC. The negative associations were indicated between BMI and walking steps (p=.03) as well as features with OSA and walking steps (p=.04). Thus, BMI and OSA were included in the regression analysis to estimate the walking steps achieved during walking trials. In addition, Bland-Altman plots demonstrated no overestimation and underestimation of variability in the difference between actual and estimated walking steps developed by using BMI and OSA. Obesity and sleep problem are potentially detrimental to walking performance (i.e., fewer walking steps) in individuals with DS. Thus, individuals with DS may adopt a slow walk speed due to the increased balance deficits and physical fatigue that result from obesity and sleep fragmentation, respectively. Exercise interventions, which have the potential to reduce obesity and OSA, are recommended to improve the accomplishment of PWC in individuals with DS.

Classification of Physical Activity Cut-Points and the Estimation of Energy Expenditure During Walking Using the GT3X+ Accelerometer in Overweight and Obese Adults

ABSTRACTThis study establishes tri-axial activity count (AC) cut-points for the GT3X+ accelerometer to classify physical activity intensity in overweight and obese adults. Further, we examined the accuracy of established and novel energy expenditure (EE) prediction equations based on AC and other metrics. Part 1: Twenty overweight or obese adults completed a 30 minute incremental treadmill walking protocol. Heart rate (HR), EE, and AC were measured using the GT3X+ accelerometer. Part 2: Ten overweight and obese adults conducted a self-paced external walk during which EE, AC, and HR were measured. Established equations (Freedson et al., 1998; Sasaki et al., 2011) overestimated EE by 40% and 31%, respectively (p < .01). Novel gender-specific prediction equations provided good estimates of EE during treadmill and outdoor walking (standard error of the estimate = .91 and .65, respectively). We propose new cut-points and prediction equations to estimate EE using the GT3X+ tri-axial accelerometer in overweight and obese adults.

Feasibility and validity of self-reported walking capacity in patients with intermittent claudication

The primary aim of this study was to assess if self-reported measures of walking limitation correlate better with a community-based assessment of maximum walking distance (MWD) than they do with laboratory-based tests in patients with intermittent claudication. A secondary aim was to examine the effect of prior objective testing on these correlations. Thirty-one patients completed three self-report tools (self-reported MWD; Walking Impairment Questionnaire [WIQ]; Estimation of Ambulatory Capacity by History-Questionnaire [EACH-Q]) immediately before and approximately 1 week after a series of objective tests (incremental treadmill walking test, 6-minute walk test, 1-hour global positioning system [GPS] recording of a community walk). We analyzed the feasibility of the self-report tools in terms of number of errors and their correlation (r) with objective measures. The correlations of self-report tests to GPS-MWD (range, .579-.808) were consistently higher than with the treadmill test (range, .310-.584) and 6-minute walk test (range, .414-.613). The WIQ had the highest proportion of errors, both at first and second completion (58% and 42%, respectively), compared with self-reported MWD (23% and 13%, respectively) and the EACH-Q (6.5% and 13%, respectively). Correlations were improved with the second set of self-report tests (range, .310-.595 to .414-.808). The fact that all self-report tools correlated better with a community-based measure of MWD using GPS than with laboratory results confirms that they measure what they aim to: community-based MWD. In addition, prescription of a community walk might help patients to better estimate their walking limitation.

Influence of codeine on lobeline-induced respiratory reflexes and sensations and on ventilation with exercise in healthy subjects

In 15 healthy subjects, the effect of 60 mg oral codeine and placebo was examined on intravenously injected lobeline-elicited respiratory reflexes and sensations. Its influence was also studied on ventilation and appearance of distressful respiratory sensations with modest but incremental exercise. After placebo, tachypnoea and respiratory sensations were evoked with 12.1 ± 1.9 μg/kg of lobeline i.v. (mean threshold dose) and after codeine, by significantly higher doses i.e., 18.0 ± 3.1 μg/kg (P < 0.05). Additionally after codeine, in response to incremental doses of lobeline the respiratory reflex was notably attenuated and the magnitude of respiratory sensations, subdued. Dry cough seen in 66% of the subjects with suprathreshold doses of lobeline i.e., 22.0 ± 3.4 μg/kg (mean), appeared post codeine, with significantly higher doses i.e., 27.0 ± 3.9 μg/kg (mean) (P < 0.05) and in a fewer subjects (60%). Mean increase in minute ventilation at the end of 8 min of incremental treadmill walking after codeine was 21% less than after placebo (P < 0.05); 60% of the subjects continued to walk for an additional 4 min and the onset of respiratory discomfort was delayed by 1-5 min. This is the first report of an attenuation of lobeline-elicited respiratory reflexes and sensations that are attributable to J receptors (pulmonary C fibres) by a pharmacological entity. It also suggests that codeine decreased these receptors' known contribution to respiratory augmentation and motor inhibition during exercise, which was seen as a delay in the onset of, and a decrease in the magnitude of respiratory discomfort during treadmill walking and an increase in the duration walked by more than half the subjects.

Perceived exertion and heart rate models for estimating metabolic workload in elite British soldiers performing a backpack load-carriage task

Identifying field measures to estimate backpack load-carriage work intensity in elite soldiers is of interest to the military. This study developed rating of perceived exertion (RPE) and heart rate models to define metabolic workload for a backpack load-carriage task valid for a population of elite soldiers using serial data. Male soldiers (n = 18) from the British Parachute or Special Air Service Regiment completed an incremental treadmill walking and (or) running protocol while carrying a 20-kg backpack. Heart rate, RPE, and oxygen uptake were recorded at each incremental stage of the protocol. Linear mixed models were used to model the RPE and heart rate data in the metric of measured peak oxygen uptake. Workload was accurately estimated using RPE alone (SE = 6.03), percentage of estimated maximum heart rate (%E-MHR) (SE = 6.9), and percentage of measured maximum heart rate (%M-MHR) (SE = 4.9). Combining RPE and %E-MHR resulted in a field measure with an accuracy (SE = 4.9) equivalent to the %M-MHR model. We conclude that RPE, %E-MHR, and %M-MHR provide accurate field-based proxy measures of metabolic workload in elite British soldiers performing a backpack load-carriage task. The model is accurate for the metabolic range measured by these serial data for the backpack load-carriage task.

Cardiocirculatory and metabolic responses at different walking intensities

Objectives: Although walking is a common physical activity, scientifically based training guidelines using standardised tests have not been established. Therefore this explorative study investigated the cardiovascular and metabolic load resulting...

The Effects Of Incremental Treadmill Walking On Skeletal Muscle Oxygenation In Older Cardiovascular Rehabilitation Participants

Pulse oximetry is commonly used to monitor arterial oxygen saturation (SpO2) during exercise in individuals with cardiovascular disease. However, many of these individuals often exhibit poor exercise tolerance despite normal SpO2 values. We propose that near-infrared spectroscopy (NIRS), a non-invasive method of estimating skeletal muscle oxygen saturation (StO2), may be more suitable for monitoring acute exercise responses in select patient populations. PURPOSE To examine the effects of incremental treadmill walking on SpO2, StO2, and calf blood flow (BF) in healthy elderly individuals (CON; n=20; 58±6 yr), individuals with coronary artery disease (CAD; n=14; 67±7 yr), and individuals with peripheral artery disease (PAD; n=5; 68±6 yr). METHODS SpO2 and StO2 were assessed before, during, and after an incremental treadmill test. The treadmill protocol consisted of seven possible stages with a constant speed of 2.0 mph and 3.5% increases in grade for each three-minute stage. Calf BF was assessed with venous occlusion plethysmography before and five minutes after the treadmill test. ANOVA with repeated measures were used to analyze the data. RESULTS There were no significant group differences at rest for StO2 (CON: 73±15%; CAD: 71±16%; PAD: 68±21%), SpO2 (CON: 97±1%; CAD: 97±1%; PAD: 97±2%), or BF (CON: 1.7±0.7; CAD: 1.3±0.5; PAD: 1.3±0.5; units = ml blood 100 ml tissue−1 min−1). Treadmill walking induced significant increases in BF for all groups (122%, 106%, and 132% for CON, CAD, and PAD, respectively; all p < 0.001), but did not significantly alter SpO2 in any group. The PAD group exhibited significantly shorter walking times than both the CON and CAD groups (14.4 vs. 20.1 and 19.1 min, respectively; p < 0.05), most likely due to StO2 values that were significantly lower than the CON and CAD groups during multiple stages of treadmill testing (each p < 0.05). CONCLUSIONS Although the three groups had similar SpO2 and BF responses to incremental treadmill walking, the PAD group had significantly lower StO2 values, indicating that skeletal muscle dysfunction is a major limiting factor on exercise capacity in these individuals. Thus, NIRS may be a more useful tool than pulse oximetry for monitoring the effects of acute and chronic exercise on those with PAD.

The Effects Of Incremental Treadmill Walking On Skeletal Muscle Oxygenation In Older Cardiovascular Rehabilitation Participants

Pulse oximetry is commonly used to monitor arterial oxygen saturation (SpO2) during exercise in individuals with cardiovascular disease. However, many of these individuals often exhibit poor exercise tolerance despite normal SpO2 values. We propose that near-infrared spectroscopy (NIRS), a non-invasive method of estimating skeletal muscle oxygen saturation (StO2), may be more suitable for monitoring acute exercise responses in select patient populations. PURPOSE To examine the effects of incremental treadmill walking on SpO2, StO2, and calf blood flow (BF) in healthy elderly individuals (CON; n=20; 58±6 yr), individuals with coronary artery disease (CAD; n=14; 67±7 yr), and individuals with peripheral artery disease (PAD; n=5; 68±6 yr). METHODS SpO2 and StO2 were assessed before, during, and after an incremental treadmill test. The treadmill protocol consisted of seven possible stages with a constant speed of 2.0 mph and 3.5% increases in grade for each three-minute stage. Calf BF was assessed with venous occlusion plethysmography before and five minutes after the treadmill test. ANOVA with repeated measures were used to analyze the data. RESULTS There were no significant group differences at rest for StO2 (CON: 73±15%; CAD: 71±16%; PAD: 68±21%), SpO2 (CON: 97±1%; CAD: 97±1%; PAD: 97±2%), or BF (CON: 1.7±0.7; CAD: 1.3±0.5; PAD: 1.3±0.5; units = ml blood 100 ml tissue−1 min−1). Treadmill walking induced significant increases in BF for all groups (122%, 106%, and 132% for CON, CAD, and PAD, respectively; all p < 0.001), but did not significantly alter SpO2 in any group. The PAD group exhibited significantly shorter walking times than both the CON and CAD groups (14.4 vs. 20.1 and 19.1 min, respectively; p < 0.05), most likely due to StO2 values that were significantly lower than the CON and CAD groups during multiple stages of treadmill testing (each p < 0.05). CONCLUSIONS Although the three groups had similar SpO2 and BF responses to incremental treadmill walking, the PAD group had significantly lower StO2 values, indicating that skeletal muscle dysfunction is a major limiting factor on exercise capacity in these individuals. Thus, NIRS may be a more useful tool than pulse oximetry for monitoring the effects of acute and chronic exercise on those with PAD.

PREDICTING VO2MAX OF OLDER ADULTS FROM OXYGEN UPTAKE EFFICIENCY DURING THE CS-PFP FUNCTIONAL FITNESS TEST

The direct measure of maximal oxygen consumption (VO2max) in older adults is problematic insofar as many cannot achieve a reliable maximum work capacity. Yet the assessment of maximum capacity is somewhat relevant for the purpose of discussing the extent to which activities of daily living utilize one's reserve for work capacity. Data from Hollenberg & Tager (2000) suggest that the Oxygen Uptake Efficiency Slope (OUES) (i.e., slope of the log of ventilation plotted against VO2) is a very reliable index of cardiorespiratory capacity in older adults with and without disease. Moreover, they showed that the OUES could be derived during incremental sub-maximal work. The purpose of this investigation was to compare the OUES as derived during incremental sub-maximal treadmill walking (according to the procedures of Hollenberg & Tager) to the OUES collected during the performance of the CS-PEP functional fitness test battery. Therefore we utilized the Cosmed K4b portable metabolic cart to collect breath gases in 5 older adults (age-range 74–95) during incremental treadmill walking (3 min stages, terminating at an RPE > 15) and during the performance of the CS-PFP functional fitness test. Subsequent examination of the regression line of log Ventilation vs. VO2 reveal only marginally weaker correlations for the CS-PFP derived slopes (Rsqare = 0.78–0.93) as compared to the treadmill derived slopes (Rsquare = 0.81–0.92). Moreover, the resultant OUES slopes as derived from the CS-PFP data varied from the treadmill derived values by 1–5%. In conclusion we suggest that the OUES can be successsfully derived during the performance of the CS-PFP, further enhancing its utility and offering an economy of testing whereby physical function data and maximal capacity can be reliably and simultaneously assessed. Sponsored in part by the LaBoR Health Excellence Fund.

Near infrared muscle spectroscopy in patients with Friedreich's ataxia.

Friedreich's ataxia is a progressive neurodegenerative disorder of the afferent cerebellar pathways associated with mitochondrial dysfunction at the cellular level. We have used noninvasive continuous near infrared muscle spectroscopy (NIRS) to investigate the delivery and utilization of oxygen in response to exercise in this disorder. Patients performed an incremental treadmill walking protocol in which levels of muscle deoxygenation or oxygenation were continuously measured in the medial calf muscle. The kinetics of recovery from exercise-induced deoxygenation, called the half-time of recovery (t(1/2)) were determined. The t(1/2) was prolonged in patients with Friedreich's ataxia compared with controls, and the degree of prolongation correlated with the length of the shorter GAA repeat, a genetic measure that correlates with the age of onset of disease. The t(1/2) also correlated inversely with patient age and with the maximum treadmill speed attained. Several patients also displayed features consistent with inadequate oxygen utilization by muscle. These results suggest that NIRS may be an effective tool for monitoring the biochemical and functional features of Friedreich's ataxia in parallel.

VARIABILITY OF PHYSIOLOGICAL AND PERCEPTIVE RESPONSES TO EXERCISE IN THE CHRONIC FATIGUE SYNDROME

2060 The chronic fatigue syndrome (CFS) is a condition known to have a cyclic aetiology, yet the exact nature or cause of either the fatigue or its fluctuation is uncertain. Eight subjects diagnosed with CFS completed an incremental treadmill walking test to volitional exhaustion on four separate occasions, each one week apart. Submaximal and maximal oxygen uptake (VO2), heart rate (HR), blood lactate (BLa) and rating of perceived exertion (RPE) were recorded on each occasion. The mean intra-subject coefficient of variation (CV) of VO2peak was 11.8 ± 5.6% (range 8.0 - 25.2%) indicating a high degree of variability in the point of volitional exhaustion from week to week. Although the CV for ventilatory threshold (VT) was slight (2.1 ± 0.6%), RPE at VT was highly variable (26.2 ± 6.7%). All results for each individual were expressed as a change from baseline (week 1) for all subsequent data analysis. Significant (p<0.05) correlations were observed between the change in VO2peak and the change in HRpeak (r=0.94) and BLapeak (r=0.75) suggesting that the variation in volitional exhaustion was not the result of changes in cardiac insufficiency or lactate accumulation. However, a significant correlation was also observed between the change in VO2peak and the change in RPE at VT (r=−0.85) suggesting that altered perceptions of exertion may be responsible for the variation in volitional exhaustion. These data suggest that the fatigue associated with CFS may be due, at least in part, to a central rather than a peripheral aetiology.

ESTIMATING ENERGY EXPENDITURE WITH MINUTE BY MINUTE HEART RATE MONITORING IN TASKS ASSOCIATED WITH WILDLAND FIREFIGHTING

1408 The purpose of this study was to estimate upper (UB) and lower body (LB) energy expenditure (EE) with minute by minute heart rate monitoring (HRM) for comparison with actual UB and LB field EE measured by indirect calorimetry (Aerosport KB1-C). HR, VO2, and RER were measured during laboratory incremental treadmill walking, and simulated fire line construction to develop linear regression equations (HR vs. VO2 and HR vs. RER) for each subject (N=13) and activity. Overall data was used to produce UB and LB group regression equations to estimate EE. Subjects completed a field hike (1.21 km) and a field dig trial (6 min) while wearing a chest strap monitor to record HR each minute during the field activities. Field HR values were integrated into the appropriate upper or lower body regression equations to estimate EE. (Table)TableThese results demonstrate accurate predictions of LB EE from minute by minute HRM using the individual and group regression equations. Neither method provided an accurate prediction of UB EE. This may in part be due to a lack of specificity of the lab simulated dig trial, thereby establishing inaccurate UB HR/VO2 relationships compared to actual field exercise. Further research is needed to examine extraneous variables which affect the HR/VO2 relationship such as environmental and core temperature, hydration status, and the effects of caffeine or nicotine. Supported by DAMD17-96-1-6329