
How to use heart rate to quantify your fitness training intensityRaphael Brandon provides another approach to determining your maximum heart rate which takes into consideration your sport and age. Articles often detail elite and complex aerobic training methods to boost endurance performance, V02max and lactate threshold. These articles typically refer to target training intensities and heart rates to achieve, say, a new 10K or marathon best; they recommend highintensity training, with very high target heart rates, to complement the longer "steadystate" sessions at more moderate intensities. However, using target training intensities and heart rates are also useful for those of us whose aerobic training is aimed at improving general health and fitness, or as general conditioning for a recreational sport.
In this more modest form, aerobic training involves an endurance activity, such as cycling, running or rowing, performed continuously for a certain amount of time, usually 30 to 40 minutes. It is recommended that if this kind of activity is performed threetofive times a week, then it will bring about optimum benefits. If you do more you will get fitter, but as a general rule, 35 x 30 to 40 minutes a week yields a good fitness reward for the amount of time invested, and so is optimal for general fitness needs. It is also advisable that with this kind of aerobic training the exercise intensity should be moderately hard. The American College of Sports Medicine (ACSM) officially recommends that the optimal intensity is between 60% and 80% of V0_{2} max. V0_{2} max is the maximum amount of oxygen, in millilitres, one can use in one minute per kilogram of weight. It is the standard measure of aerobic fitness. However, it is impossible to maintain maximal oxygen use for longer than about 8 to 10 minutes. Thus, for general fitness training, one should aim to be at 60 to 80% of maximum capacity and maintain this level for 30 to 40 minutes. This intensity is comparable to the training levels elite athletes would use on their "steady state" sessions. When performing some of the more advanced interval sessions, elite athletes will be at intensities greater than 85% V0_{2} max. At the other extreme, activity at an intensity of 40% V0_{2} max is likely to improve health but won't significantly improve aerobic fitness. Take the case of JoeIt is possible to estimate your exercise intensity as a percentage of V0_{2} max from your training heart rate. This is very useful, for elite and recreational athlete alike, because by monitoring heart rate you can quantify your training effort and target the correct intensity for maximum benefits. These calculations are possible because of the linear relationship between heart rate (HR) and oxygen use (V0_{2}) with increasing rates of work. For example, if Joe is sitting down doing nothing, his resting HR might be 70 bpm. At this HR, V0_{2} would be at its baseline level, which is approximately 3.5 ml/kg/min. If Joe starts to walk, his HR may increase to around 100 bpm as the V0_{2} goes up to cope with the extra energy demand. If Joe now breaks into a jog his HR will go higher again, up to 140bpm, say, as V0_{2} increases further. Then, if Joe runs as fast as he can for three minutes, his HR might go up to its maximum of 190 bpm. At this point, Joe will have reached his V0_{2} max. Therefore, at V0_{2} max, HR is also maximum, and at a percentage of V0_{2} max, there is a corresponding percentage of HR_{max}, this relationship has been shown to hold true across sex, age and exercise type. The ACSM suggest that 40% V0_{2} max corresponds to 55% HR_{max}, 60% V0_{2} max corresponds to 70% HR_{max}, 80% V0_{2} max corresponds to 85% HR_{max} and 85% V0_{2} max corresponds to 90% HR_{max}. These values are derived from various studies, which have compared V0_{2} with HR and determined regression equations for % HR_{max} versus % V0_{2} max. Revising the ACSM formulaThese target values of % HR_{max} provide a means of quantifying exercise intensity to optimise training results. If the optimal training intensity is 60 to 80% V0_{2} max then, according to the ACSM, the corresponding optimal training HR is 70 to 85% Maximum Heart Rate (HR_{max}). However, the ACSM Position Stand (1990)^{[5]} made these official recommendations in 1990. Since then, a study by David Swain and his USA based research team, Swain et al.^{[1]}, has criticised the mathematical methods used to derive the regression equations in previous research. Using more correct statistical procedures, they reexamined the relationship between % V0_{2} max and % HR_{max} and found that the ACSM formula underestimates HR at the target values of % V0_{2} max. Their results led to a regression equation of % HR_{max}= 0.64 x % V02 max + 37. This means that 40% V0_{2} max corresponds to 63% HR_{max}, 60% V0_{2} max corresponds to 75% HR_{max}, 80% V0_{2} max corresponds to 88% HR_{max}, and 85% V0_{2} max corresponds to 92% HR_{max}. Therefore, using these results, the optimal training HR range for general aerobic fitness is 75 to 88% HR_{max}, significantly higher than the 70 to 85% HR_{max} from the ACSM. For Joe, with his HR_{max} at 190 bpm, using Swain et al.^{[1]}, his target HR range is 143168 bpm, as opposed to the ACSM's recommended range of 133161 bpm. Improved research from Swain et al.^{[1]} thus suggests that training heart rates should be pushed up a little to 75 to 88% HR_{max} to bring about optimum results. For elite athletes, Swain et al.^{[1]} showed that % HR_{max} for the same % V0_{2} max was slightly higher compared to average. Therefore, for steadystate training, an HR range of 7789% V0_{2} max would be appropriate for an elite athlete. For advanced interval training, the intensity must be above 85% V0_{2} max or above 92% HR_{max}. For example, during a session comprising 6 x 800m runs at 5K pace, the training intensity will be at 9095% V0_{2} max. This would correspond to a training HR of 95 to 97% HR_{max}. We can see from these examples that knowing accurately what % HR_{max} corresponds to a target % V0_{2} max is very useful for both the average and the elite athlete. By using the formula derived by Swain et al.^{[1]}, we can calculate a target training heart rate for the particular goal of the individual. So, how precisely is HR_{max} calculated? The easiest and bestknown method is to use the formula 220  age. This is the method recommended in the ACSM guidelines. However, the actual derivation for this regression equation has never been published. It is used since it is a simple way to get a good estimate of HR_{max}. In an attempt to be more accurate, numerous crosssectional studies have been done to investigate the relationship between HR_{max}, age and other factors. A paper by Londeree and Moeschberger^{[2]} from the University of Missouri Columbia collates the data from all these studies to bring together the findings. What they show is that HR_{max} varies mostly with age, but the relationship is not a linear one. Thus the 220  age formula is slightly inaccurate. For adults under 30, it will overestimate HR_{max} and for adults over 45, it will underestimate HR_{max}. This is especially true for welltrained over45s whose HR_{max} does not reduce as much as with sedentary individuals of the same age. Londeree and Moeschberger^{[2]} suggest an alternative formula of 206.3  (0.711 x age). Similarly, Miller et al.^{[3]} from Indiana University propose the formula 217  (0.85 x age) as a suitable HR_{max} calculation. In my experience, it is the Miller formula, which gives appropriate estimates when calculating HR_{max} from age alone.
Swimming Heart rates are lowerLonderee and Moeschberger also looked at other variables to see if these had an effect on HR_{max}. They found that neither sex nor race makes a difference. However, HR_{max} does vary with activity and fitness level. Studies have shown that HR_{max} on a treadmill is consistently 5 to 6 beats higher than on a bicycle ergometer and 2 to 3 beats higher than on a rowing ergometer. Heart rates while swimming are significantly lower still, around 14bpm than for treadmill running. Running and Versaclimber, Brabler & Blank (1995)^{[4]} show similar HR_{max}. Londeree and Moeschberger also found fitness levels lead to a variation in HR_{max}. Elite endurance athletes and moderately trained individuals will have an HR_{max} three or four beats lower than a sedentary individual. However, as already stated, this is only true for young athletes, welltrained over50s are likely to have a higher HR_{max} than that which is average for their age. This is of utmost relevance to those using the rower or bicycle or those who are very fit, since training HRs will have to be calculated differently. To do this, Londeree and Moeschberger offer us another formula, a slightly more complicated interactive equation to calculate HR_{max} for different ages, activities and fitness levels. However, it is very difficult to use without a calculator and a degree in mathematics! My own suggestionHaving outlined various methods for calculating HR_{max}, I would recommend the following, which combines the Miller formula [3] with the research from Londeree and Moeschberger^{[2]}:
One question that you may be justified in asking is "who cares?" Will all these complicated percentages and formulae make a difference, when the old ACSM recommendations are so straightforward? The point is that, if you want to use heart rate monitors, it serves little purpose unless you know ACCURATELY what training intensity the measurement represents. For example, a 45yearold jogging to get fit should maintain 60% V0_{2} max for a 20 to 30 minutes continuous run. Using the old ACSM, recommendations, he would be aiming for 70% HR_{max}. HR_{max} would be estimated at 175 bpm using the 220  age formula. This gives a target training HR of 123 bpm. However, the jogger's HR_{max} is more likely to be 179 bpm, and following Swain et al. target training HR should be 75% HR_{max}. These two changes give a revised training HR of 134 bpm, a massive 11 bpm difference in target HR. If our 45yearold had followed the old recommendations, his or her training would have been below optimal intensity, at 50% V0_{2} max, and he or she would not have got the most from the invested training time. These inaccuracies can also disadvantage the elite athlete. For example, a 25yearold elite cyclist using the 220  age formula may think his HR_{max} is 195 bpm. However, it is more likely to be only 188 bpm. This could mean he is overestimating target training HR for certain sessions, which can be undesirable if mileage rather than intensity is the aim of the session. The takehome message of this article is a word of warning if you use traditional calculations to quantify training intensifies. If 60% V0_{2} max is the minimum intensity for aerobic fitness improvements, then 75% and not 70% HR_{max} is the minimum training target HR. However, using a range of 7588% HR_{max} for training targets is probably best. To calculate HR_{max}, the simple 220  age formula is not always accurate. The alternative formulas provided will give you more accurate estimates. For beginners and individuals training for a healthy fitness or for a recreational sport, I recommend that you calculate your HR_{max} for your chosen training activity and then the 75% HR_{max} training target. During your workouts, use an HR monitor or take your pulse and make sure that you put in enough effort to get your HR to the required level for a fitness benefit. For elite athletes, use the new formulae to accurately calculate your maximum and target heart rates. Remember that tough interval sessions need to be tough, so make sure your HR reaches around 95% HR_{max}. However, sometimes you need to keep training moderate, so aim for 7789% HR_{max} for steadystate training. References
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