Exercise+Training

Position Statements
Both the National Heart Foundation's Position Statement on Lipid Management--2005 (NHF) and the American National Cholesterol Education Program Adult Treatment Panel III (NCEP ATPIII) identify the following lipid and lipoprotein abnormalities as major risk factors in coronary heart disease (CHD) -
 * low density lipoprotein-cholesterol (LDL-C) > 100mg/dL
 * high density lipoprotein-cholesterol (HDL-C) < 40mg/dL

So, to reduce the risk of coronary heart disease (CHD), therapies dealing with dyslipidaemias principally target these two measures.

NCEP ATPIII recommends **Therapeutic Lifestyle Changes** (TLC) as a first line intervention before the administration of pharmacological agents. TLC includes the following components -
 * **Reduced intakes of saturated fats and cholesterol**
 * **Therapeutic dietary options for enhancing LDL lowering (plant stanols/sterols and increased viscous [soluble] fiber)**
 * **Weight reduction**
 * **Increased regular physical activity**

NCEP ATPIII suggests that "regular physical activity reduces very low-density lipoprotein (VLDL) levels, raises HDL cholesterol, and in some persons, lowers LDL levels". NCEP ATP III recommends that regular physical activity become a routine component in management of high serum cholesterol.

The National Heart Foundation Position Statement focuses heavily on the pharmacotherapies, despite the associated risks of commonly prescribed pharmaceuticals (see Medical and Clinical Considerations). It does acknowledge the utility of "at least 30 minutes per day of moderate-intensity physical activity on most, and preferably all days of the week" in improving lipid profiles. The position statement also acknowledges that increased physical activity can lower blood pressure, reduce insulin resistance, and favorably influence cardiovascular function. However, the NHF suggests that 'lifestyle management" therapies (including diet and exercise) may require "ongoing support to be sustainable". The authors of the NHF Position Statements see a clear role for Dietitians and Exercise Physiologists to provide that support to patients for both preventative and therapeutic interventions for dyslipidaemias.

While the NHF and NCEP ATPIII endorse exercise as therapy, the ideal exercise prescription remains rather elusive. A broad range of studies have investigated the effect of increased physical activity on lipid and lipoprotein levels. These studies have targeted specific sub-populations and in some cases have found specific effects, and in others found no significant effect of different exercise modalities and/or intensities.

**General Exercise Principles**

For patients with only marginally compromised or normal lipid profiles, exercise interventions can be utilised as a preventative measure to maintain or improve their lipid profile. In many such patients, the acute effects of exercise training include lowering of triglyceride concentrations, increased lipoprotein enzyme activity, improved glycaemic control and increases in HDL-C concentrations. Regular daily physical activity tends to translate into chronic positive effects on these aspects of the lipid profile and when patients succeed with weight loss a broader range of positive effects are commonly observed. Varady and Jones (2005) provide a comprehensive review of studies that combine various modalities of the Therapeutic Lifestyle Changes and conclude that combination lifestyle therapies are an "efficacious, preliminary means of improving cholesterol levels" that should be implemented in place of drug therapy when cholesterol levels fall just above the normal range.

Other chronic disease issues will tend to constrain the prescription of exercise training as a therapeutic intervention for many patients experiencing hyperlipidaemias. For patients with other coronary heart disease risk factors, their ability to safely engage in a training may be severely limited and a very gradual introductory phase to training may be required. Of the Therapeutic Lifestyle Changes mentioned above, the initial emphasis may need to be on reducing saturated fat and cholesterol intake, other dietary interventions to enhance LDL lowering, and weight reduction prior to any serious increase in physical activity levels.

Unfortunately, prescribing exercise in combination with other lifestyle changes may still not provide the solution. The most frequently observed chronic alteration in lipid profile following exercise (with and without weight loss) is an increase in HDL-C. However, Joy and Hegele (2008) have recently questioned the utility of simply seeking increases in HDL-C concentration. They describe the complexity of HDL-C metabolism and suggest that the functional quality of the circulating HDL-C is more important than the HDL-C concentration alone. Fortunately they found no evidence that HDL-C based therapies will be ineffective in assisting with atherosclerosis - but they have flagged the need for future research to more deeply investigate the effect of exercise interventions on characteristics of the HDL-C rather than simply estimating its concentration.

Adherence
As with any population, adherence to exercise programming can be an issue. In the case of hyperlipidaemias, the chronic effect of increased regular physical activity can be somewhat delayed. Patients may see other positive outcomes of a regimen of TLC, prior to seeing significant change in their lipid profile. But the evidence suggests that after a period of 12 weeks of increased activity and diet, positive effects on the lipid profile should emerge in the majority of patients.

The Evidence - in brief
Durstine et al (2001) reviewed the literature and found - > "a careful evaluation of the literature indicates that exercise training, more often than not, results in unaltered Total Cholesterol (TC) and LDL-C levels. In some instances, regular exercise can produce small changes in TC and LDL-C of 4 to 7% in both men and women. Reductions in these lipid fractions occur with greater frequency in previously sedentary individuals and when exercise caloric expenditure exceeds1200 kcal/wk. At present, baseline levels of TC and LDL-C, changes in body weight and body fat, and exercise intensity do not seem to be determinants for exercise-induced changes in TC and LDL-C levels."

With respect to Triglycerides (TG) and HDL-C, Durstine et al (2001) concluded > "regular aerobic exercise can increase HDL-C and TG levels in men and women. The effect of exercise on HDL-C is similar in both males and females; however, TG changes are more commonly reported in males.The training effect is strongest in non-obese individuals with normal or elevated HDL-C before the exercise intervention. In contrast, baseline TG levels do not seem to impact TG responses to exercise. In addition, changes in bodyweight or body fat do not appear to be necessary for favourable exercise adaptations in these lipids. Regular exercise can raise HDL-C levels by 2 to 8 mg/L and lower TGs from 5 to 38 mg/dL in men and women. The training volumes that elicit energy expenditures ≥1200 kcal/wk are most frequently associated with elevations in HDL-C levels in both genders and reduced TG levels in men. At present, a threshold for lowering TGs in women cannot be established from the exercise training literature."

A more recent review of randomised controlled trials, Tambalis (2009), found that for aerobic training, more favourable effects on HDL-C levels followed aerobic training programs of higher intensity, and that reductions in TG, Total Cholesterol and LDL-C appeared less often. They found a trend in the resistance training studies for a positive effect on LDL-C, but with a considerable number of conflicting studies. For combined exercise training (a mix of aerobic and resistance training) Tambalis (2009) found limited studies, mainly focussed on elderly patients, with inconclusive outcomes.

The majority of literature studying the effects of exercise on dyslipidaemia and hyperlipidaemia often under prescribes exercise protocols for several reasons.

Firstly, a relatively intense exercise protocol is likely to have a high attrition rate which researchers do not benefit from as this reduces the statistical strength of the study. Secondly, researchers seek to apply a uniform exercise prescription across all subjects. Such prescriptions are often expressed in relative terms rather than absolutes, ie as %HRmax for aerobic training or % of the individual's 1RM or 8RM for resistance training. So, this approach does tend to specialise the prescription to suit the capabilities of individuals, but generally the selected intensity is probably less than many of the participants would readily tolerate.

So, when prescribing exercise in clinical practice, the exercise physiologist should treat every case on its merits and quite possibly employ an exercise prescription for many patients that's well in excess of the protocols employed in many of the studies. **The one clear message that emerges from the studies is that more is better, in terms of both volume and intensity.**

There is a large body of scientific literature examining the efficacy of various specific training regimes on lipid profiles for particular populations. Some of that literature is summarised here -
 * aerobic training ,
 * resistance training and
 * combination exercise training
 * special populations

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