The purpose of the warm-up is to prepare the muscular, nervous, cardiac, respiratory and vascular systems for the main workout. In other words, a warm-up prepares the body for the change from rest to exercise. The warm-up should be carried out at a low intensity and speed, repetition and exertion should be progressively increased. This graduated approach allows the heart to adapt to increased demand and to avoid the myocardial ischaemia and arrhythmias that may be provoked by sudden strenuous exercise (Dimsdale, et al., 1984). Strenuous exercise without a warm-up can produce ischaemic ST segment changes and arrhythmias, even in healthy individuals (ACPICR, 2003). The warm-up should include: pulse-raising exercises, mobility exercises and preparatory stretches as follows:

Pulse-Raising Exercises

These exercises gradually elevate the heart rate, thus giving the heart time to increase stroke volume and cardiac output. For patients with residual ischaemic/angina, a slow elevation will extend this threshold (BACR, 1995). During exercise, increased oxygen demands on the heart muscle are met through vasodilation of the coronary arteries, caused by local chemical changes (increase in CO2 and lactic acid). In addition, the increase in myocar-dial oxygen requirement stimulates the sympathetic nervous system to release noradrenaline, causing further vasodilation of the coronary arteries. There is an associated increase in aortic pressure, which, due to the anatomy of the coronary arteries (situated at the bottom of the aorta), forces more blood into the coronary circulation. The ability of the body to maintain an adequate blood supply is important, as energy for the cardiac muscle relies almost entirely on aerobic metabolism. For those with residual ischaemia, this increase in oxygen supply will extend the threshold.

The warm-up should last for 15 minutes (BACR, 1995, ACSM, 2001), to allow for the necessary coronary adaptations to occur. The warm-up should gradually increase the heart rate to approximately 20 beats-min-1 below the target HR recommended for the individual (Fardy, et al., 1998) no more than 11 on the Borg RPE (Borg, 1998).

During the warm-up, arm exercises should be introduced gradually. Arm exercises above the head must be introduced slowly, so as to avoid sudden increases in SBP and RPP, as discussed in Chapter 3. The increase is due to the smaller muscle mass of the upper body, compared to the larger muscle mass of the lower body (Schwade, et al., 1977).

Mobility Exercises

Mobility exercises, e.g. shoulder rolls and knee bends should be gradually introduced, interspersed with pulse-raising exercises. The purpose of mobility exercises is to prepare specific joints and muscles that will be used during the main workout. Mobility exercises also provide an opportunity for skill rehearsal. Skill rehearsal introduces exercises that are used in the cardiovascular section of the class and are especially relevant for new patients in the group.

Preparatory Stretches

Including stretching during the warm-up is a controversial issue. At present, there is little scientific evidence to support preparatory stretches during the warm-up. A preparatory stretch component in most exercise classes is common, but there is sparse evidence to suggest that stretching is more effective than a good warm-up (Anderson O., 2000). However, there is evidence that relates muscle tightness to muscle injury (Stickler, et al., 1990). Regular stretching will increase and improve flexibility, which in turn improves movement quality (Anderson B., 2000). Preparatory stretching aims to prepare the main muscle groups that will be used in the conditioning component. Cold muscle will have less blood flow and, therefore, it will be relatively inelastic and potentially at a higher risk of strain (Stickler, et al., 1990).

Preparatory stretching should be static and held at the end of available range position, until there is a sensation of mild discomfort, but not pain (AACVPR, 1999). Although there is some debate on the frequency and duration of preparatory stretching, current recommendations are for a static stretch held for approximately 10 seconds with four repetitions of each muscle group (ACSM, 2001). If stretches are included, they should be interspersed with pulse-raising exercises in order to maintain an elevated heart rate and prevent venous pooling and a drop in BP.

104 Exercise Leadership in Cardiac Rehabilitation

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