"(beats per minute) Step 2. Calculate exercise intensity ACSM guidelines = 55 – 90% of HR max Lower target (55%) = 190 × 55% = 190 × 0.55 = 104.5 bpm (we would round this up to 105 bpm) Upper target (90%) = 190 × 90% = 190 × 0.90 = 171 bpm This formula gives us an idea of maximum heart rate, but we must remember that it is just an estimate and not completely accurate. Therefore using this method, according to ACSM guidelines, Mariella sho uld exercise at a heart rate somewhere between 105 and 171 bpm . This is quite a wide range so, depending on her fitness levels, you would need to decide whether to prescribe Mariella exercise to the upper or lower end of this scale. Please note that ther e are online calculators available to calculate all of this information for you. Once such calculator can be found at: http://www.sparkpeople.com/resource/calculator_target.asp The HRR method is thought to be more accurate than the percentage of maximal heart rate method because it takes the individual’s resting heart rate into account. The formula for calculating HRR can be seen in Box 2. The ACSM recommends that to improv e aerobic fitness, exercise intensity should be set at either 40 – 85 per cent of (HRR) or 55 – 90 per cent of maximum heart rate (HR max ) (Pollock et al., 1998). These ranges are deliberately broad to reflect different levels of fitness; that is, someone with relatively low levels of fitness who has just started an exercise programme may need to work on the lower end of the scale, whereas someone who has a higher level of fitness, perhaps who has been exercising for a while, may need to work at an intensity towards the upper end of the scale. This demonstrates the importance of progression in an exercise programme. Example 2: Heart Rate R eserve Method Case study: ‘Mariella’, age 30 Step 1. Calculate maximum heart rate (HR max ) Estimated HR max = 220 - age = 220 – 30 = 190 bpm (beats per minute) Step 2. Measure resting heart rate (HR rest ) You would measure this either using a heart rate monitor or manually, using your fingers. Ideally it should be measured first thing in the morning. Let's imagine that Mariella's HR rest has been measured"