three papers presented at ACSM's annual meeting
Mistretta, J.L., et al. 2004. Medicine & Science in Sports & Exercise, 36 (5, Suppl.), S4.
Background. Social opportunities during exercise—such as having a partner for conversation—provide a distraction and may encourage adherence. As long as exercise intensity is sufficient relative to participants’ fitness levels, benefits can be derived.
The Study. Exercise physiologists at the University of Scranton in Scranton, Pennsylvania, examined the cardiometabolic responses of treadmill running at a self-selected speed that allowed for 20 minutes of conversation in 2-minute intervals. Results were then compared with 70% of measured VO2max.
Methods. Mistretta and colleagues determined the running speeds during conversation for 24 physically active volunteers (11 males, 13 females; mean age 20.2 years). Each subject then underwent a 6-minute submaximal steady-state treadmill test at his or her conversation running speed. The average speed was 6.6 miles per hour (mph) for the males, 5.8 mph for the females. Cardiometabolic responses were measured during this test. Finally, a maximal treadmill test was administered to determine aerobic power (VO2max, or maximum volume of oxygen consumed—in milliliters—per kilogram of body weight per minute [ml/kg/min]). The respiratory quotient, or RQ—the ratio of oxygen consumed to carbon dioxide produced—was also determined for each participant. (An RQ exceeding 1.0 represents maximum or near-maximum exertion.) The testing phases took place on separate occasions. Mean body mass index was 25.8 for the males, 21.7 for the females.
Results. Maximal treadmill test results included heart rates within 5 beats per minute (bpm) of age-predicted maximum (bpm averaged 199 for males, 194.5 for females). VO2max results averaged 48.1 for males (RQ = 1.2), 42.8 for females (RQ = 1.1). Combined group heart rate at 70% VO2max was not significantly different from submaximal steady-state heart rate during conversation (168 vs. 171 bpm). However, VO2 values were significantly higher for conversation running than they were at 70% VO2max (34.3 vs. 31.7 ml/kg/min).
Male vs. female heart rate and VO2 results were significantly different during the steady-state test (176.9 vs. 168.2 bpm and 36.9 vs. 32.0 ml/kg/min, respectively) but not at 70% VO2max (169 vs. 168 bpm and 33.8 vs. 30.0 ml/kg/min, respectively).
Researchers’ Conclusions. These findings suggest that conversation during aerobic exercise may lead to a higher exercise intensity (in this case, 86% of heart rate maximum [HRmax], 77% of VO2max) than the American College of Sports Medicine’s mid-range recommendation (HR = 75%, VO2max = 70%). While previous research has supported conversation during exercise as an acceptable method of achieving recommended intensity, this study suggests objective physiological measures (i.e., heart rate and VO2) are more appropriate and desirable for judging exercise intensity.
Comments. This is one of the first objective evaluations of the effect of conversation on exercise VO2 and heart rate response. The exercise VO2 response during conversation running appears to have been only marginally higher than during nonconversation exercise. However, for exercisers who are already near lactate threshold (at approximately 70% of VO2max), casual chatting with a fitter partner during exercise might surely jeopardize exercise duration for the less fit individual.
The investigators’ suggestion to use “objective physiological measures”—heart rate and VO2—rather than a conversation-based pace to achieve recommended exercise intensity does not seem wholly practical for population-based exercise recommendations.
Van Pelt, R.E. 2004. Medicine & Science in Sports & Exercise, 36 (5, Suppl.), S1.
Purpose. This study’s primary aim was to determine the independent relations of central (upper-body) and peripheral (lower-body) adiposity to the metabolic syndrome (a cluster of risk factors, including obesity, high blood lipids and glucose intolerance).
The Study. This study involved more than 300 postmenopausal women between the ages of 50 and 85 years with varying degrees of total and regional adiposity.
Methods. Van Pelt measured total, trunk and leg fat using dual-energy x-ray absorptiometry (DEXA) and abdominal subcutaneous and visceral fat using computed tomography (CT). Markers of insulin resistance and dyslipidemia were determined from oral glucose tolerance tests (OGTT) and fasting lipid/lipoprotein measurements, respectively. Primary outcome measures of interest were fasting insulin (INS), area under the curve for insulin (INSa), product of the OGTT glucose and insulin areas (INSa × GLUa), serum triglycerides (TG) and high-density lipoprotein cholesterol (HDL-C).
Results. Central adiposity (DEXA trunk fat, CT abdominal fat) and peripheral adiposity (DEXA leg fat) were independently related to markers of the metabolic syndrome. Although central fat was associated with unfavorable levels of INS, INSa, INSa × GLUa, TG and HDL-C, peripheral fat showed a favorable independent association with these markers of hyperinsulinemia and dyslipidemia. Furthermore, the relation of DEXA trunk fat to risk factors was explained by visceral, but not subcutaneous, abdominal adiposity, whereas DEXA leg fat was favorably related to these risk factors after controlling for total abdominal adiposity.
Researcher’s Conclusions. Peripheral fat, unlike central fat, is predictive of reduced risk for the metabolic syndrome. It is not known whether leg fat per se confers protection against metabolic dysfunction or whether the tendency to store fat in the lower body is simply a marker of, for example, favorable genetic predisposition. The results here are consistent with previous evidence that peripheral adiposity (thigh girth) is associated with reduced incidence of type 2 diabetes and ischemic heart disease.
Comments. This is not the first study to show the different risk levels associated with central and peripheral fat. Central fat (abdominal visceral fat) is more atherogenic, primarily for three reasons. Compared to peripheral fat stores, central abdominal fat stores
- have more immediate access to the liver (where most atherogenic lipoproteins are made) via the portal vein
- are more likely to increase blood coagulability
- have a higher rate of adrenaline-induced release (mobilizations)
Peripheral fat stores do not possess these metabolic/atherogenic properties. Although excess peripheral fat may appear unsightly, it doesn’t represent any particular level of diabetes or heart disease risk and may in fact be associated with lower risk, although more research is required to substantiate this finding.
Wallace, B.P., Sforzo, G.A., & Swensen, T. 2004. Medicine & Science in Sports & Exercise, 36 (5), S249.
Background. The elliptical trainer (ET) has received little research attention, especially in comparison to other modalities.
The Study. Exercise physiologists at Ithaca College in Ithaca, New York, compared physiological responses during ET and treadmill (TM) exercise at three intensities.
Methods. Responses were gauged using ratings of perceived exertion (RPE) on a Borg RPE scale range of 6–20. Twenty-four physically active males (
= 12) and females ( = 12) completed maximal and submaximal exercise sessions on both modalities. Maximal tests were used to obtain mode-specific VO2max, HRmax and RPEmax. The submaximal exercise sessions, which followed 48 hours after maximal testing, consisted of three 6-minute exercise bouts at RPE-gauged intensities of 11 (fairly light), 13 (somewhat hard) and 15 (hard) on each modality. Each subject’s RPE intensity order was preassigned in a partially randomized, balanced order.
Results. TM elicited greater VO2max and HRmax responses than did ET. Submaximal exercise data comparing mode, gender and RPE intensity level revealed that TM elicited greater submaximal VO2, HR and energy expenditure (EE) across the three RPE-gauged intensities. No modality-related gender differences were observed.
Researchers’ Conclusions. The results of this study demonstrated that TM produces greater EE than ET, with less strain or feeling of exertion. Movement patterns associated with ET may elicit localized leg fatigue that affects perception of intensity, thereby leading to lower EE at a given RPE. Despite EE differences, ET provides a respectable, low-impact exercise alternative to TM running. If maximizing EE with the lowest perception of effort is the goal, however, then TM is the recommended modality. Exercise prescriptions using RPE should consider this information when switching between modalities.
Comments. A similar study from University of Nebraska researchers (Cook, Heelan & Krueger 2004, p. S249 in the same journal) reported that in 18 college students (nine males, nine females), energy expenditure was not different between the two modes for either gender. However, in the Cook study the subjects exercised at self-selected moderate RPE levels of 12–13 (rather than a preassigned RPE). In that study, heart rates elicited in all subjects were significantly higher on the EL than on the TM, even though perceived exertion ratings were not significantly different.
These two studies show the variability of responses using perceived exertion indices—which, by definition, are subjective. Despite the high comparative energy expenditure claims extolled by some manufacturers of elliptical machines, these machines offer at best equivalent caloric expenditures to treadmill exercise for given perceived effort.
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