 Heart rate can be defined as the number of times that the heart contracts per minute in order to sustain blood supply to the working body. It is an objective measure of the cardiovascular demand placed on the body. For our purposes, the cardiovascular system will be defined as the heart and blood vessels which carry nutrients and oxygen to the working tissues (muscles, organs) of the body and removes carbon dioxide and waste.
A wide range of exercise intensities and modes can be monitored through the measurement of heart rate. This includes sub-maximal exercise, where a steady state heart rate is desired, to repeated bouts of high intensity exercise in which heart rate is rapidly increased and decreased repeatedly for short or long durations. Therefore, whenever interpreting the heart rate response, it must be viewed based on the objective(s) of the training session.
Interpreting Heart Rate
A very stable heart rate pattern can be determined during exercise. A decrease or increase in heart rate for a given training intensity can indicate an improved or decreased tolerance to the training session. In order to properly assess the training session, heart rate should be monitored during the exercise and recovery period. During the recovery period, the time needed to return to a heart rate associated with the “recovery zone” (often defined as less than 120 beats per minute) should also be noted. Improvements in the time to return to this recovery zone can also indicate that adaptations to training have taken place. Lastly, when assessing heart rate, variables such as hydration level, weather (temperature, humidity) and stress can all greatly affect the heart’s response and should be taken into account.
Monitoring the Response to Steady State Exercise
Heart rate is most commonly assessed in endurance sports or for an aerobic training session where a steady state heart rate and/or pace are desired for greater than three minutes. When performing a steady state training session, work must be maintained for at least three minutes in order to obtain a heart rate that is truly reflective of the cardiovascular system and the training demand.
When the duration of an exercise bout is shorter than three minutes, the heart rate response is not complete due to a lag in response time by the cardiovascular system. Training plans for most aerobic training programs are based on intensity and the intensity is described by heart rate being divided into training zones. Training zones can be set based on percentages of the maximum heart rate as described below:
When training works, it results in a reduced heart rate at a given work intensity. As a result, higher workloads are then feasible in a given training zone. However when a higher heart rate is demonstrated, this means the athlete is not adapting to the training program, environmental conditions, or can be a sign of illness or poor recovery from a previous training bout.
Monitoring the Response to Repeated Bouts of High Intensity Exercise
Whether training for repeated bursts of speed as might be required in team sport or an individual sport with speed components, the ability to explode and recover quickly over and over again is critical to success in these sports. They require a very high level of fitness, often termed anaerobic endurance. Anaerobic endurance athletes can repeatedly sustain bursts of 20-40 seconds in duration while also executing a very technical skill.
Heart rate can be monitored in these sport situations for average heart rate, peak heart rate. how quickly the heart rate returns to baseline following a burst in play, and whether over time the athlete can actually maintain a lower heart rate for the same training session or game play. The more rapidly a high heart rate can return to recovery levels, the more fit the athlete is at the level play being performed. In the same sense, when swimmers, runners, triathletes and other individual sport athletes perform interval or sprint sessions, the highest heart rate obtained for each repetition and the time needed to return to recovery levels is indicative of adaptation to the training load.
A favorable response to a training bout that is repeated over a four week training block is reported in the table below. It can be noted that adaptation has occurred based on a reduction in recovery heart rate at one minute following the repetition and a lower heart rate for each repetition. In addition, the rating of perceived exertion (RPE) by the athlete was lower following the four week training period:
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