Heart rate response during intervaltype exercise

Interval circuit exercise is specifically beneficial to individuals with low functional capacity, left ventricular dysfunction or concomitant pulmonary or peripheral circulatory disease exercise limitations (Cachovan, et al., 1976; Maass, et al., 1983; Meyer, et al., 1990; Cooper, 2001).

The use of interval circuit exercise is a typical feature in the UK for phase III and IV rehabilitation programmes. Interval training permits the patient to produce a greater amount of work in a training session if the training periods are spaced between periods of lower intensity work. These lower intensity bouts, called active recovery (AR) periods, are between 30 seconds and 1 minute in duration. A deconditioned patient may only be able to maintain a training intensity exercise for a few minutes before becoming too fatigued to continue.

Other practical reasons for using the interval circuit format include the lack of specialist exercise facilities, where rehabilitation gymnasia are multipurpose, and the area needs to be set up and cleared for a variety of uses. This is addressed by the characteristics of interval training which allows for the use of very basic exercise equipment (hand weights, steps, shuttle walks, callisthenic-type movements, etc.) and typically results in an interval approach where patients exercise for no more than three minutes at each station. The total duration of exercise, however, is aimed at accumulating the recommended minimum of at least 20 minutes of aerobic activity (ACSM, 2000).The AR intervals are typically no more than one minute. The progression is to gradually remove the active-rest intervals towards achieving at least 20 minutes of continuous activity.

For patients using interval circuit training, the differences in HR response compared to continuous activity need to be acknowledged. It has long been known that it takes at least two minutes for HR to rise and level off, following the initiation of constant sub-maximal exercise workload (Saltin, et al, 2000). This time lag is a function of the response time of the sympathetic neuro-humoral regulation of HR, relative to the required systemic circulatory and metabolic demands. Because interval training often has exercise stations lasting less than two minutes, the theoretical matching of HR to muscular work output will not occur. If patients are attaining their aerobic target HR in this short period (<2mins) they will actually be working at an intensity that would elicit an HR above their target, if the activity were sustained continuously (>2mins).

Inadvertently, this is beneficial, because it is metabolically challenging to the skeletal muscle. In addition, there is a built-in safety margin for the HR. Before HR begins to approach its critical level, the patient starts to decrease intensity as part of AR. However, over the course of a rehabilitation session, there is cardiovascular drift and an increased likelihood of muscular fatigue. This latter point could cause a potential loss of sense of achievement for the patient if the intensity is too high. With too high an intensity, the accumulation of lactic acid will prolong both metabolic recovery and heart rate recovery (McArdle, et al., 2001). This is due to both the raised aerobic metabolism needed to clear the lactate from the system and lactate's sympathetic nervous system stimulating properties. The concept of the cool-down is discussed in more depth in Chapter 5 on programme design.

Figure 3.3 provides an example of the differences in an individual's HR at the same treadmill speeds during one-minute, compared to three-minute stages. In this individual, when the intensity requires greater than 60% HRmax

Heart rate at a given MET level for 1 and 3 min durations

Heart rate at a given MET level for 1 and 3 min durations

Heart Rate Based Interval Training

Figure 3.3. The difference in heart rate at the same treadmill work rate (metabolic equivalents; METs) on two separate tests; one test where the duration at each stage was one minute and the other for three minutes at each stage.

(JP Buckley (unpublished) 2004, Exercise Laboratory, School of Health and Rehabilitation, Keele University, UK.)

Figure 3.3. The difference in heart rate at the same treadmill work rate (metabolic equivalents; METs) on two separate tests; one test where the duration at each stage was one minute and the other for three minutes at each stage.

(JP Buckley (unpublished) 2004, Exercise Laboratory, School of Health and Rehabilitation, Keele University, UK.)

(120 beats • min J), the difference in HR by prolonging exercise at a given work rate from one minute to three minutes is as much as 10 beats-min-1.

Run for Your Life The Health Benefits Of Treadmills

Run for Your Life The Health Benefits Of Treadmills

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