Special needs to prescribe exercise intensity for scientific studies

Abstract

There is clear evidence regarding the health benefits of physical activity. These benefits follow a dose-response relationship with a particular respect to exercise intensity. Guidelines for exercise testing and prescription have been established to provide optimal standards for exercise training. A wide range of intensities is used to prescribe exercise, but this approach is limited. Usually percentages of maximal oxygen uptake (VO(2)) or heart rate (HR) are applied to set exercise training intensity but this approach yields substantially variable metabolic and cardiocirculatory responses. Heterogeneous acute responses and training effects are explained by the nonuniform heart rate performance curve during incremental exercise which significantly alters the calculations of %HR(max) and %HRR target HR data. Similar limitations hold true for using %VO(2max) and %VO(2)R. The solution of these shortcomings is to strictly apply objective submaximal markers such as thresholds or turn points and to tailor exercise training within defined regions.

Figure 1

Schematic representation of first- and second- turn points of selected variables (La blood lactate concentration; VE: ventilation; VE/VO₂: equivalent for oxygen uptake; VE/VCO₂: equivalent for carbon dioxide output; HR: heart rate; B_f: breathing frequency) and distinct phases (Ph 1–3) of energy supply determined from young healthy male subjects. Ph 1: no increase of blood lactate concentration above baseline during constant load exercise. Ph 2: increased but steady state blood lactate concentration during constant load exercise. Ph 3: continuous increase of blood lactate concentration during constant load exercise leading to early termination of exercise.

Figure 2

Accuracy of target training heart rate dependent on the time course of the Heart Rate Performance Curve. The same relative intensity of 85% HR_max (usual upper limit) gives different work load related to the anaerobic threshold (LTP₂) [29]. Subject (A) 85% HR_max is well below HR LTP₂; subject (B) 85% HR_max is already above HR LTP₂.

Figure 3

Error of estimate for percent heart rate reserve (HRR) compared to %HR at the second lactate turn point (LTP₂) as well as the error of estimate for percent HR_max related to the deflection of the heart rate performance curve (kHR) [29, 30] in healthy young male and female sports students, young obese subjects, older healthy subjects, and patients after myocardial infarction [31].

Figure 4

Mean blood lactate concentration (La) during constant load exercise in trained subjects applying controlled 70%–75% of VO_2max (unpublished results).