John P. Porcari

Estimation of VO2max from a one-mile track walk, gender, age, and body weight.

The purpose of this investigation was to explore an alternative field test to estimate maximal oxygen consumption (VO2max) using a one-mile walk test. VO2max was determined in 343 healthy adult (males = 165, females = 178) subjects 30 to 69 yr using a treadmill protocol (mean +/- SD: VO2max = 37.0 +/- 10.7 ml X kg-1 X min-1). Each subject performed a minimum of two, one-mile track walks as fast as possible. The two fastest walks (T1, T2) with elapsed times within 30 s were used for subsequent analyses. Heart rates were monitored continuously and recorded every one-quarter mile. Multiple regression analysis (best sub-sets) to estimate VO2max (l X min-1) yielded the following predictor variables: track walk-1 time (T1); fourth quarter heart rate for track walk-1 (HR 1-4); age (yr); weight (lb); and sex (1 = male, 0 = female). The best equation (N = 174) was: VO2max = 6.9652 + (0.0091*WT) - (0.0257*AGE) + (0.5955*SEX) - (0.2240*T1) - (0.0115*HR1-4); r = 0.93, SEE = 0.325 l X min-1. Comparing observed and estimated VO2max values in a cross-validation group (N = 169) resulted in r = 0.92, SEE = 0.355 l X min-1. Generalized and sex-specific equations to estimate VO2max (ml X kg-1 X min-1) were also generated. The accuracy of estimation as expressed by SEE was similar among the equations. The results indicate that this one-mile walk test protocol provides a valid sub-maximum assessment for VO2max estimation.

Regulation of pacing strategy during athletic competition.

Background Athletic competition has been a source of interest to the scientific community for many years, as a surrogate of the limits of human ambulatory ability. One of the remarkable things about athletic competition is the observation that some athletes suddenly reduce their pace in the mid-portion of the race and drop back from their competitors. Alternatively, other athletes will perform great accelerations in mid-race (surges) or during the closing stages of the race (the endspurt). This observation fits well with recent evidence that muscular power output is regulated in an anticipatory way, designed to prevent unreasonably large homeostatic disturbances. Principal Findings Here we demonstrate that a simple index, the product of the momentary Rating of Perceived Exertion (RPE) and the fraction of race distance remaining, the Hazard Score, defines the likelihood that athletes will change their velocity during simulated competitions; and may effectively represent the language used to allow anticipatory regulation of muscle power output. Conclusions These data support the concept that the muscular power output during high intensity exercise performance is actively regulated in an anticipatory manner that accounts for both the momentary sensations the athlete is experiencing as well as the relative amount of a competition to be completed.

Consistency of the talk test for exercise prescription.

Implications for Muscle Lipid Metabolism and An accumulation of intramuscular lipid has been reported with obesity and linked with insulin resistance. The purpose of this paper is to discuss: 1) mechanisms that may be responsible for intramuscular lipid accumulation with obesity, and 2) the effects of common interventions (weight loss or exercise) for obesity on skeletal muscle lipid metabolism and intramuscular lipid content. Data suggest that the skeletal muscle of morbidly obese humans is characterized by the preferential partitioning of lipid toward storage rather than oxidation. This phenotype may, in part, contribute to increased lipid deposition in both muscle and adipose tissue, and promote the development of morbid obesity and insulin resistance. Weight loss intervention decreases intramuscular lipid content, which may contribute to improved insulin action. On the other hand, exercise training improves insulin action and increases fatty acid oxidation in the skeletal muscle of obese/morbidly obese individuals. In summary, the accumulation of intramuscular lipid appears to be detrimental in terms of inducing insulin resistance; however, the accumulation of lipid can be reversed with weight loss. The mechanism(s) by which exercise enhances insulin action remains to be determined.INTRODUCTION/PURPOSE The Talk Test has been shown to be well correlated with the ventilatory threshold, with accepted guidelines for exercise prescription, and with the ischemic threshold. As such, it appears to be a valuable although quite simple method of exercise prescription. In this study, we evaluate the consistency of the Talk Test by comparing responses during different modes of exercise. METHODS Healthy volunteers (N = 16) performed incremental exercise, on both treadmill and cycle ergometer. Trials were performed with respiratory gas exchange and while performing the Talk Test. Comparisons were made regarding the correspondence of the last positive, equivocal, and first negative stages of the Talk Test with ventilatory threshold. RESULTS The %VO2peak, %VO2 reserve, %HRpeak, and %HR reserve at ventilatory threshold on treadmill versus cycle ergometer (77%, 75%. 89%, and 84% vs 67%, 64%, 82%, and 74%) were not significantly different than the equivocal stage of the Talk Test (83%, 82%, 86%, and 80% vs 73%, 70%, 87%, and 81%). The VO2 at ventilatory threshold and the last positive, equivocal and negative stages of the Talk Test were well correlated during treadmill and cycle ergometer exercise. CONCLUSIONS The results support the hypothesis that the Talk Test approximates ventilatory threshold on both treadmill and cycle. At the point where speech first became difficult, exercise intensity was almost exactly equivalent to ventilatory threshold. When speech was not comfortable, exercise intensity was consistently above ventilatory threshold. These results suggest that the Talk Test may be a highly consistent method of exercise prescription.INTRODUCTION Obesity and weight gain are negative prognostic factors for breast cancer survival. Physical activity (PA) prevents weight gain and may decrease obesity. Little information exists on PA levels among cancer survivors. We assessed PA, including the proportion of breast cancer survivors engaging in recommended levels, by categories of adiposity, age, disease stage, and ethnicity in 806 women with stage 0-IIIA breast cancer participating in the Health, Eating, Activity, and Lifestyle Study. METHODS Black, non-Hispanic white, and Hispanic breast cancer survivors were recruited into the study through Surveillance Epidemiology End Results registries in New Mexico, Western Washington, and Los Angeles County, CA. Types of sports and household activities and their frequency and duration within the third yr after diagnosis were assessed during an in-person interview. RESULTS Thirty-two percent of breast cancer survivors participated in recommended levels of PA defined as 150 min x wk(-1) of moderate- to vigorous-intensity sports/recreational PA. When moderate-intensity household and gardening activities were included in the definition, 73% met the recommended level of PA. Fewer obese breast cancer survivors met the recommendation than overweight and lean breast cancer survivors (P < 0.05). Fewer black breast cancer survivors met the recommendation compared with non-Hispanic white and Hispanic breast cancer survivors (P < 0.05). CONCLUSIONS Most of the breast cancer survivors were not meeting the PA recommendations proposed for the general adult population. Efforts to encourage and facilitate PA among these women would be an important tool to decrease obesity, prevent postdiagnosis weight gain, and improve breast cancer prognosis.PURPOSE To derive a regression equation that estimates metabolic equivalent (MET) from accelerometer counts, and to define thresholds of accelerometer counts that can be used to delineate sedentary, light, moderate, and vigorous activity in adolescent girls. METHODS Seventy-four healthy 8th grade girls, age 13 - 14 yr, were recruited from urban areas of Baltimore, MD, Minneapolis/St. Paul, MN, and Columbia, SC, to participate in the study. Accelerometer and oxygen consumption (.-)VO(2)) data for 10 activities that varied in intensity from sedentary (e.g., TV watching) to vigorous (e.g., running) were collected. While performing these activities, the girls wore two accelerometers, a heart rate monitor and a Cosmed K4b2 portable metabolic unit for measurement of (.-)VO(2). A random-coefficients model was used to estimate the relationship between accelerometer counts and (.-)VO(2). Activity thresholds were defined by minimizing the false positive and false negative classifications. RESULTS The activities provided a wide range in (.-)VO(2) (3 - 36 mL x kg x min) with a correspondingly wide range in accelerometer counts (1- 3928 counts x 30 s). The regression line for MET score versus counts was MET = 2.01 +/- 0.00171 (counts x 30 s) (mixed model R = 0.84, SEE = 1.36). A threshold of 1500 counts x 30 s defined the lower end of the moderate intensity (approximately 4.6 METs) range of physical activity. That cutpoint distinguished between slow and brisk walking, and gave the lowest number of false positive and false negative classifications. The threshold ranges for sedentary, light, moderate, and vigorous physical activity were found to be 0 - 50, 51- 1499, 1500 - 2600, and >2600 counts x 30 s, respectively. CONCLUSION The developed equation and these activity thresholds can be used for prediction of MET score from accelerometer counts and participation in various intensities of physical activity in adolescent girls.

The Physiological Responses to Walking with and without Power Poles™ on Treadmill Exercise

Power Poles are specially constructed, rubber-tipped ski poles designed for use during walking. Using Power Poles simulates the arm motion of cross-country skiing, thus increasing the muscle mass used during walking. This study investigated the potential increases in exercise intensity and energy cost associated with the use of walking poles. Thirty-two apparently healthy volunteers (16 men and 16 women) between the ages of 19 and 33 years participated. Each completed a treadmill maximal oxygen consumption (VO2max) test and two randomly assigned, submaximal walking trials (one with poles and one without poles) on separate days. Each walking trial was conducted on a level treadmill, for 20 minutes, at an identical self-selected pace. Expired gases, heart rate in beats per minute (bpm), and ratings of perceived exertion (RPE) were recorded each minute. Results between trials were compared using repeated measures analysis of variance and Tukeys post hoc tests. It was found that walking with poles resulted in an average of 23% (4.4 ml.kg-1.min-1) higher VO2, 22% higher caloric expenditure (1.5 kcal.min-1), and 16% (18 bpm) higher heart rate responses compared to walking without poles on a treadmill. RPE values averaged 1.5 units higher with the use of the poles, and the pattern of responses between conditions was similar for men and women. It is concluded that the use of Power Poles can increase the intensity of walking at a given speed and, thus, may provide additional training benefits to walkers.

Perception of fatigue during simulated competition

BACKGROUND Previous studies suggest that the rating of perceived exertion (RPE) increases during steady-state, open-loop exercise in proportion to the relative time to fatigue. This suggests that RPE is scalar and integrates physiological status and homeostatic disturbances. PURPOSE This study assessed the relationship between the rate of change in RPE, and relative distance in time trials at distances of 2.5, 5, and 10 km. It also assessed the rate of change in RPE during 5-km time trials while breathing hypoxic air. METHODS The subjects were well-conditioned cyclists. In part 1, each subject completed habituation time trials, and then randomly ordered time trials at each distance. The category ratio RPE was measured in 10% increments throughout each trial. In part 2, each subject completed three 5-km time trials while breathing different inspired gas mixtures (FiO2 = 0.2093 throughout the trial, FiO2 = 0.15 between 2 and 4 km, and FiO2 = 0.15 between 2.5 and 4 km). RPE was measured at 10% increments. RESULTS In part 1, when RPE was plotted against relative distance, there was no significant difference in the growth of RPE at proportional distances. In part 2, the decrease in power output during the hypoxic segments was sufficient that the growth of RPE was the same at each proportional distance. In both parts of the study, an RPE of 5 (hard) was achieved after 20% of the time trial distance, and an RPE of 8 was achieved after 80% distance. CONCLUSIONS This study supports the hypothesis that RPE increases similarly in relation to relative distance, regardless of the distance performed, and it suggests that the perception of effort has scalar properties.

Cranberry extract inhibits low density lipoprotein oxidation

Cranberry juice consumption is often used for the treatment of urinary tract infections, but the effect of cranberry juice on heart disease has not been investigated. We evaluated how a cranberry extract containing 1,548 mg gallic acid equivalents/liter (initial pH=2.50) affected low density lipoprotein (LDL) oxidation induced by 10 micromolar cupric sulfate. When LDL oxidation took place in the presence of diluted cranberry extracts, the formation of thiobarbituric acid reactive substances (TBARS) and LDL electrophoretic mobility were reduced. LDL electrophoretic migration was also reduced when the cranberry extract had a pH of 7.00 prior to dilution. This study suggests that cranberry extracts have the ability to inhibit the oxidative modification of LDL particles.

Walking for Health and Fitness

Recent studies have linked regular physical activity with reduced likelihood of developing coronary heart disease. Even low- and moderate-intensity exercise such as walking, when carried out consistently, is associated with important cardiovascular health benefits. Walking has also been shown to reduce anxiety and tension and aid in weight loss. Regular walking may help improve cholesterol profile, help control hypertension, and slow the process of osteoporosis. Recent physiological studies have demonstrated that brisk walking provides strenuous enough exercise for cardiovascular training in most adults. A recently developed submaximal 1-mile walk test provides a simple and accurate means for estimating aerobic capacity and guiding exercise prescription. These new insights and tools will assist the clinician in the prescription of safe and effective walking programs.

The talk test as a marker of exercise training intensity.

PURPOSE Correlative data have suggested that the Talk Test (TT) may be a surrogate of the ventilatory threshold (VT). This study examined manipulations of either the VT or exercise protocol to test the hypothesis that the TT and VT are related in a robust way, adequate for exercise prescription. METHODS Healthy young adults participated in 4 independent series of experiments designed to decrease (blood donation) or increase (training) VT, or to systematically vary the exercise intensity above and below VT. These interventions were matched to responses of the TT. RESULTS The changes in the exercise intensity at VT and at the last positive stage of the TT matched each other following both blood donation and training. When exercise intensity was varied above and below VT, the predicted ability to speak was well matched to observations of the TT. Predictive errors biased toward passing the TT when exercise intensity was greater than VT. The time required for the result of TT to become negative when exercise intensity was more than VT, decreased with increasing intensity but averaged more than the 2 minutes that has been used in previous studies. CONCLUSIONS This study confirms the robust relationship between VT and the TT during various interventions and suggests that the TT is suitable for exercise prescription.

Pattern of developing the performance template

Background: The pattern of energy expenditure during sustained high-intensity exercise is influenced by several variables. Data from athletic populations suggest that a pre-exercise conceptual model, or template, is a central variable relative to controlling energy expenditure. Aims: The aim of this study was to make systematic observations regarding how the performance template develops in fit individuals who have limited specific experience with sustained high-intensity exercise (eg, time trials). Methods: The study was conducted in four parts and involved measuring performance (time and power output) during: (A) six 3 km cycle time trials, (B) three 2 km rowing time trials, (C) four 2 km rowing time trials with a training period between trials 2 and 3, and (D) three 10 km cycle time trials. All time trials were self-paced with feedback to the subjects regarding previous performances and momentary pace. Results: In all four series of time trials there was a progressive pattern of improved performance averaging 6% over the first three trials and 10% over six trials. In all studies improvement was associated with increased power output during the early and middle portions of the time trial and a progressively greater terminal rating of perceived exertion. Despite the change in the pattern of energy expenditure, the subjects did not achieve the pattern usually displayed by athletes during comparable events. Conclusions: This study concludes that the pattern of learning the performance template is primarily related to increased confidence that the trial can be completed without unreasonable levels of exertion or injury, but that the process takes more than six trials to be complete.

Hemodynamic Responses During Aerobic and Resistance Exercise

PURPOSE Resistance training has become an accepted part of cardiac rehabilitation programs. Because of the potential for a high afterload to have a negative impact on left ventricular function, there has been concern regarding the safety of resistance training for patients with congestive heart failure. METHODS This study addressed this concern by studying 12 healthy volunteers, 12 patients with stable coronary artery disease, and 12 patients with stable congestive heart failure during upright cycling at 90% of ventilatory threshold, and during one set of 10 repeated leg presses, shoulder presses, and biceps curls at 60% to 70% of 1-repetition maximum. Left ventricular function was measured by echocardiography. RESULTS The pattern of changes in heart rate, blood pressure, left ventricular ejection fraction, wall thickness, and left ventricular internal diameters was similar across all three groups of subjects, although there were large differences in absolute values. Despite elevations in diastolic and mean arterial pressures during resistance exercise, there was no evidence of significant rest-to-exercise deterioration in left ventricular function during leg press (ejection fraction, 60%-59%, 56%-55%, and 38%-37%), shoulder press (66%-65%, 59%-53%, and 38%-35%), or biceps curls (63%-58%, 53%-54%, and 35%-36%), as compared with cycle ergometry (63%-69%, 51%-57%, and 35%-42%) in the healthy control subjects, the patients with coronary artery disease, and the patients with congestive heart failure, respectively. CONCLUSIONS Left ventricular function remains stable during moderate-intensity resistance exercise, even in patients with congestive heart failure, suggesting that this form of exercise therapy can be used safely in rehabilitation programs.