Research

Exercise Intensity and Heart Disease Dose Response for Strength Development Risk Safety of Weight Loss Drugs

Exercise Intensity and Heart Disease Risk

Lee, I-Min, et al. 2003. Relative intensity of physical activity and risk of coronary heart disease. Circulation, 107, 1110.

Current exercise recommendations encourage adults to engage, almost daily, in ≥ 30 minutes of at least moderate-intensity physical activity (requiring ≥ 3 METs [metabolic equivalents]). This much energy expenditure equals about 1,000 kilocalories (kcal) per week.

Defining intensity using an absolute scale in METs may be limited because it neglects variations in physical fitness. An activity requiring a particular MET value commands greater physical effort from a less fit person than it does from someone more fit. It is unknown whether moderate-intensity exercise, relative to an individual’s capacity, is associated with reduced coronary heart disease (CHD) rates.

Study. Exercise epidemiologists from the Harvard School of Public Health followed 7,337 men (mean age = 66 years) from 1988 to 1995. At baseline, men reported their actual activities and, using the Borg Scale, their perceived levels of exertion when exercising (relative intensity). During follow-up, 551 men developed CHD.

Results. After multivariate adjustment, the relative risks of CHD among men who perceived their exercise exertion to be “moderate,” “somewhat strong” and “strong” or more intense were 0.86 (i.e., 14 percent relative reduction), 0.69 and 0.72, respectively (p = 0.02), compared with the risk for men who rated their exertion as “weak” or less intense. This inverse association extended to men not fulfilling current recommendations—i.e., expending < 1,000 kcal per week in physical activity or not engaging in activity requiring ≥ 3 METs (p = 0.03 and 0.007, respectively).

Researchers’ Conclusions. There is an inverse association between relative intensity of physical activity (an individual’s perceived level of exertion) and risk of CHD, even among men not satisfying current recommendations for activity. Future recommendations for “moderate”-intensity physical activity may need to consider individual fitness levels instead of globally prescribing activities requiring ≥ 3 METs.

Comments. Inactive adults should make it their first priority to build up gradually to at least 1,000 kcal of moderate exercise per week—for example, three 45-to-50-minute sessions per week at moderate intensity (40-60 percent of peak aerobic capacity). Exercise of this volume and intensity can substantially reduce CHD risk. After clients have safely adhered to such a program for 2 to 4 weeks, then gradually increasing the overall intensity of exercise—for example, from 50-60 percent to 65-75 percent of aerobic capacity—may further reduce CHD risk, according to this study and a number of other trials.

Dose Response for Strength Development

Rhea, M.R., et al. 2003. A meta-analysis to determine the dose response for strength development. Medicine & Science in Sports & Exercise, 35, 456-64.

Identifying a quantifiable dose-response relationship for strength training is important for prescribing proper training programs.

Study. Exercise scientists at Arizona State University carried out a meta-analysis of 140 studies with a total of 1,433 effect sizes (ES). (ES is a standard unit for measuring and interpreting changes; it allows for comparisons of different training methods within a single study.) The purpose of the meta-analysis was to identify a quantitative dose-response relationship for strength development. To do this, the researchers calculated the magnitude of gains elicited by various levels of training intensity, frequency and volume, thus clarifying the effort-to-strength-benefit ratio.

The analysis included studies that employed a strength training intervention and contained data necessary to calculate ES. The primary investigator read and coded each study for the following variables: gender, age, training frequency, mean training intensity, number of sets performed and participants’ training status. Frequency was determined by the number of days per week participants trained a particular muscle group. Intensity was coded as the average percent of one-repetition maximum (1 RM) used throughout the training program. Volume was recorded as the number of sets performed (per muscle group) during each workout. The participants’ training status was either trained or untrained. Participants must have been weight training for at least 1 year before the study to be considered trained.

Results. Training at a mean intensity of 60 percent of 1 RM elicited maximal gains in untrained individuals. For those who were trained, the most effective intensity was 80 percent of 1 RM. Untrained participants experienced maximal gains by training each muscle group 3 days per week. In trained individuals, maximal gains resulted from training each group 2 days per week (Figure 1). Performing four sets per muscle group elicited maximal gains in both trained and untrained individuals (Figure 2).

Researchers’ Conclusions. The dose-response trends identified in this analysis support the theory of progression in resistance program design. They can be useful for developing training programs designed to optimize the effort-to-strength-benefit ratio.

Comments. It is apparent that lower-frequency, lower-intensity training with fewer sets can improve strength. However, for maximal and continued adaptations over time, additional work at higher intensities is necessary. Fitness professionals should ascertain how much strength their clients need or want to gain, and then explain the effort-to-benefit ratio. Clients wanting to improve strength- or endurance-specific performance may benefit from doing more sets with higher loads. For those desiring overall improvement in musculoskeletal fitness and functionality, fewer sets and moderate loads may be sufficient.

Safety of Weight Loss Drugs

Shekelle, P.G., et al. 2003. Efficacy and safety of ephedra and ephedrine for weight loss and athletic performance: A meta-analysis. Journal of the American Medical Association, 289, 1537-45.

Consumers sometimes take ephedra or ephedrine to lose weight or enhance athletic performance, but the efficacy and safety of these compounds are uncertain.

Study. Researchers at the University of Southern California and several other local health care institutions set out to assess whether ephedra and ephedrine are safe and effective means of losing weight and enhancing athletic performance. The investigators searched nine databases using the terms ephedra, ephedrine, adverse effect, side effect, efficacy, effective and toxic. The search included unpublished trials and non-English-language documents.

The researchers assessed (1) controlled trials in which ephedra or ephedrine was used for weight loss or athletic performance and (2) case reports of adverse events associated with such use (obtained from the U.S. Food and Drug Administration MedWatch program). For weight loss, eligible studies were human studies with at least 8 weeks of follow-up; for athletic performance, they were studies with no minimum follow-up. Eligible case reports documented that ephedra or ephedrine was consumed within 24 hours prior to an adverse event or that ephedrine or an associated product was found in blood or urine. They also excluded other potential causes.

Of the 530 articles screened, Shekelle and colleagues included 52 controlled trials and 65 case reports in the adverse events analysis. Of more than 18,000 other case reports screened, 284 underwent detailed review.

Results. Treatment did not last longer than 6 months in any of the weight loss trials. Pooled results for trials comparing a placebo with ephedrine (n= 5), ephedrine and caffeine (n = 12), ephedra (n = 1), and ephedra and caffeine-containing herbs (n = 4) yielded estimates of weight loss (more than a placebo) of 0.6, 1.0, 0.8 and 1.0 kilograms (kg) per month, respectively.

The investigators found no trials showing ephedra’s effect on athletic performance; the seven trials examining ephedrine’s effect were too heterogeneous to synthesize. Safety data from 50 trials yielded estimates of 2.2- to 3.6-fold increases in the risk of heart palpitations and psychiatric, autonomic or gastrointestinal symptoms. The majority of case reports were insufficiently documented to allow meaningful assessment.

Researchers’ Conclusions. Ephedrine and ephedra promote modest short-term weight loss (~0.9 kg per month more than a placebo) in clinical trials. There are no data regarding long-term weight loss, and evidence to support use of ephedra for athletic performance is insufficient. Use of ephedra or ephedrine and caffeine is associated with increased risk of heart palpitations and psychiatric, autonomic or gastrointestinal symptoms.

Comments. Most individuals taking ephedra or ephedrine will not experience significant or dangerous side effects or adverse events during or after exercise. However, 5 to 6 percent of individuals are symptomatic with these drugs and have an increased probability of experiencing serious adverse events, e.g., dangerous cardiac arrhythmias (such as ventricular tachycardia). Note that cardiac arrhythmias may come on without prior symptoms. Personal trainers should take these drugs into account when reviewing client health histories and query clients on current drug use prior to physical exercise.

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Ralph La Forge, MS

IDEA Author/Presenter
Ralph La Forge, MS, is a physiologist and board-certified clinical lipid specialist. He is the ma... more less
Source: Rhea, M.R., et al. Medicine & Science in Sports & Exercise, 35, 456-64.
June 2003

© 2003 by IDEA Health & Fitness Inc. All rights reserved. Reproduction without permission is strictly prohibited.

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