The purpose of this study was to provide an integrative, quantitative review of the research that has attempted to make clear the mechanisms most responsible for changes in functional capacity (FC) in patients. The meta-analytic technique proposed by Glass (1978) was used to quantify the data of numerous studies located via computer-generated citations. Many investigators have documented that improvements in FC are largely the result of complex adaptations in skeletal muscle which reflect multiple anatomic, biochemical, and hormonal alterations. Yet some investigators (Ehsani et al 1981, 1982, 1986; Hagberg et al 1983) have claimed that concomitant with peripheral adaptations, changes in FC via central or cardiac mechanisms (ie, myocardial contractility, perfusion, ejection fraction, and stroke volume) are possible with prolonged, sufficiently intense training regimens. A total of 22 effect sizes (ES) were produced from 20 studies which contained the data necessary for ES computation. The ES for studies in support of cardiac adaptations (n = 10) was 3.3 +/- 1.9, while the ES for studies documenting peripheral mechanisms (n = 10) was 3.2 +/- 1.6. This statistically nonsignificant finding indicates that FC may be similarly altered by either mechanism. However, those studies indicating adaptations via central changes used significantly more intense training programs (80% of VO2max versus 73.5% of VO2max, p < 0.05). This finding corroborates the results of Ehsani and others who isolated intensity as the critical component of the exercise prescription. In further support of this finding, differences in frequency (4.1 days/week versus 3.2 days/week), duration (39.6 min. versus 43.3), and mode of exercise (walk/jog 3.3 versus all other forms 3.1) were not significant in any of the studies. Additional analysis revealed that neither the length of the program (6 month = 3.7 versus 12 month = 3.2) nor the type of patient studied (coronary artery disease (CAD) 3.8 versus documented myocardial infarction (MI) 2.9) accounted for any differences in the type of adaptation identified. As a result of this meta-analysis, it is suggested that investigations that stratify patients according to degree of CAD, location and extent of MI, and that compare interval versus continuous training are needed to further explain how and why various adaptations occur.
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