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Heart Rate Training for Improved Running Performance

 

By Jason R. Karp, M.S.

A coach and exercise physiologist, Jason Karp is always welcome in the pages of Track Coach because of his admirable ability to explain technical concepts clearly and straightforwardly. This article elucidates the importance of heart rate measurement and why it can be extremely helpful to the coach.
 

    The heart is the symbol for our most powerful emotion, love. It is the core, the center. It can be found among the scribbles in a lovestruck girl's high school notebook, as a figure of speech when we thank people ("from the bottom of my heart"), and as a metaphor for life and death when beneath the delicate hands of a surgeon as he performs a bypass operation. Even when we salute the American flag and sing the National An- them, we place our hand over our heart as a symbol of loyalty to and respect for our country.
    The ancient Greeks may have been the first to acknowledge the existence of the heart, which they named kardia. Our words cardiac, cardiovascular, electrocardiogram (ECG or EKG), echocardiogram, and cardiologist are all derived from that word. The Greek philosopher Aristotle thought that the heart was the seat of the soul and the center of man. But it is certainly also the most extraordinary muscle in the human body. It is always working, from before we are born until we die. It has both the unique ability and responsibility of delivering the most important chemical element, oxygen, throughout the body to sustain life. And it is how our most vital body fluid, blood, is delivered to our organs and running muscles. With running, we can actually train the heart to pump more efficiently, to pump more blood (and hence, oxygen) with each beat.
    The prescription of running intensity during prolonged workouts has always been an approximate endeavor because adjustments of intensity often rely on the athlete's perception of effort. Measurements that accurately reflect the intensity of running in terms of metabolic demand, including oxygen consumption (VO2) and blood lactate, are limited to a laboratory setting. By contrast, the heartbeat-the split-second sequence of contractions of the heart's four chambers-is the most easily measured physiological indicator of running intensity, and thus offers us, as coaches, a very reliable and objective variable with which to work.

    It has been reported that the heart rate observed at slightly below the ventilatory threshold (the level of exercise beyond which the volume of carbon dioxide expired is greater than the volume of oxygen inspired) is a better indicator of the exercise intensity that can be sustained for pro- longed periods than other physiological measures such as blood lactate concentration, work output, ventilation (liters of air breathed in or out per minute), and volume of expired carbon dioxide (VCO2) (Boulay, et aI., 1997). This is good news for the coach since determining your athletes' heart rates is obviously much easier than determining their blood lactate concentrations or VO2.
    In response to physical activity, heart rate increases in a predictable manner. In fact, the relationship between exercise intensity and heart rate is an extremely linear one-the greater the intensity, the higher the heart rate, with the relationship becoming more curvilinear (heart rate begins to plateau) at very high intensities. Because of its predictability, you can use heart rate to prescribe running intensities. It can also be used to monitor your athletes' progress over time. For example, as your athletes get in better shape, they will be running at a faster pace when at the same heart rate and their heart rate will be lower when running at the same pace.

METHODS FOR DETERMINING TARGET HEART RATE
    There are generally two ways to use heart rate to determine intensity. The first is to simply take a percent- age of your athlete's maximum heart rate (max HR). The approximate max HR can be determined by subtracting an athlete's age from 220. For example, a 20-year-old's max HR would be approximately 200 beats per minute (220-20), and a target range of 70 to 80% would correspond to 140 to 160 beats per minute.
    The second method of using heart rate to calculate a target range involves the athlete's resting heart rate. This method is called the Karvonen method, named after its founder. To calculate an athlete's target heart rate, subtract resting HR from max HR before multiplying by the desired percentage. The resting HR is then added back to the product. The difference between the max HR and the resting HR is called the heart rate reserve (HRR).
    If the 20-year-old in the above example has a resting HR of 50 beats per minute, a target heart rate of 70- 80% HRR would be calculated as follows:

HRR = (220-20) - 50 = 150 beats/ min. Lower Limit = (150 x 0.70) + 50 = 155 beats/min. Upper Limit = (150 x 0.80) + 50 = 170 beats/min. The Karvonen formula is especially attractive to use since it also estimates the running intensity in relation to the athlete's maximum oxygen consumption (VO2 max). For example, 75% HRR equals 75% VO2 max. (There is about a 10% difference when comparing either %HRR or % VOmax to %max HR, however. For example, 75% HRR equals about 85% max HR.)

    When using the Karvonen method, you should retest your athlete's resting HR once every few months to recalculate a target range since resting HR decreases as cardio- vascular fitness improves. However, there is a limit as to how much the resting (or running) heart rate will decrease in response to training.
    Remind your athletes that the goal is not a heart rate of zero. The lower resting heart rate in endurance- trained runners results from a combination of an increased stroke volume (the volume of blood pumped by the heart's left ventricle with each beat) and an increased activity from the parasympathetic nervous system. Since max HR decreases with age (by about one beat/min. per year), you should also readjust the target HR as your athletes get older.
    It is important to remember that the formula "220-age" provides only an estimate of the max and may be off by more than 10-15 beats/min. All people of the same age do not have the same max HR (Wilmore & Costill, 1988). In fact, 68% of the population will have a max HR within one standard deviation of the population's average, with 95% falling within two standard deviations of the average.
    This rather large margin of error can lead to prescribing a running intensity that is either too low or too high to achieve the optimal benefit. The equation tends to overestimate max HR in highly trained runners and underestimate max HR in un- trained people. A more accurate way to determine max HR would be to measure your athlete's HR while he performs an all-out test, such as a race or a time trial.

HEART RATES FOR SPECIFIC WORKOUTS
    Once you know your athlete's actual max HR, knowing exactly what target HR to prescribe is where the task becomes complicated, since there is great variability among runners concerning how long a given percentage of max HR can be sustained. This will depend, in part, on the athlete's general physical fitness level and his specific lactate threshold (the point at which lactate begins to quickly accumulate in the muscles and blood).
    For example, a high school fresh- man coming out for the cross country team may feel discomfort after only a few minutes of running, even at 60% max HR, while a competitive college runner could run at 90% max HR without much discomfort. It is paramount, therefore, to take into account the present physical state of your athletes when prescribing running intensity. The other major factor that determines what HR you should use is the goal of individual workouts.

AEROBIC ENDURANCE
    Continuous, aerobic running lasting 30 to 60 minutes (or longer) should be performed at about 70- 75% max HR (60-65% HRR). These runs target cellular changes within the running muscles, such as increases in the number and size of mitochondria and capillaries. For this type of work- out, 70-75% max HR is all your runners need to cause those changes, Most of your athletes' running during the base phase of the training year when they are increasing weekly mileage should be done at 70-75% max HR.
    If the length of the run is well within the athlete's aerobic capacity and is a regular part of his or her training, it is possible for the heart rate to remain nearly constant throughout the run (as long as the terrain remains flat and it is not excessively hot). During very long runs, however, when glycogen levels are getting low, heart rate will begin to drift upward as the body fatigues.

LACTATE THRESHOLD
Workouts that target improvements in the lactate threshold should be performed at about 80-90% max HR. The intensity feels "comfortably hard." The more fit your athletes are, the higher their lactate threshold is in relation to max HR, and therefore the greater the intensity they will have to run at to train the lactate threshold. By raising their lactate threshold, your athletes will be able to run harder for longer periods of time. Training in this HR zone may take place in the latter portion of the base phase and the early competitive phase of the training year.

AEROBIC POWER (VO2 MAX)
While running at lower intensities is great for building an endurance base and for recovery between hard workouts, optimum improvements in aerobic fitness occur when running is performed at an intensity over 90% max HR (Wenger & Bell, 1986). This is because training at this high intensity targets improvements in VO2 max.
    Aerobic intervals (running periods lasting more than 2 minutes separated by short rest periods) are primarily used to accomplish this goal by targeting cardiac factors associated with VO2 max (e.g., stroke volume, cardiac output, heart contractility, etc.). Since VO2 max occurs at or very near 100% max HR, your athletes should perform these intervals at or very close to 100% max HR.
    Coaches need to be careful here when prescribing the intensity, because if a 6:00 mile elicits max HR surely a 5:45 mile will also elicit max HR. However, because the purpose of the workout is to target VO2 max, the goal of the workout is achieved by running the mile repeats in 6: 00 each. Running faster only serves to add more fatigue to your athlete's legs. Remember, the goal of training is to provide the least stressful stimulus that will elicit the desired adaptation. Intervals in this HR zone are typically performed during the competitive phase of your athletes' season.

ANAEROBIC GLYCOLYSIS
    Anaerobic intervals (intense running periods lasting 30 seconds to 2 minutes separated by long recovery periods) train the muscles' ability to tolerate and buffer muscle acidosis and train the recruitment of fast-twitch muscle fibers to enhance speed. Using heart rate is typically not valid in this case since your athletes will be running at a speed that is much faster than that which will elicit max HR. In addition, if the interval is short enough, HR will not even have time to increase to maximum levels.
    Table 1 summarizes the different types of workouts and their corresponding heart rate guidelines to be used during the training year. Although there are different theories and opinions among coaches concerning the precise ordering of workouts during the training year, one thing that should remain constant is that the goal of the individual workout and the corresponding heart rate should always match.
    Notice the range of heart rate percentages in the table rather than a set heart rate value for each type of workout. The reason for this is two- fold. First, not all runners will have the same heart rate at a given intensity due to differences in lactate threshold and economy, and second, during interval workouts, heart rate will drift upward as the number of repetitions increases.
    For example, if an athlete runs 6 x 800 meters in 2:30, his heart rate can be expected to be somewhat higher during the latter repetitions compared to the earlier repetitions, due to the accumulated stress of the workout. The heart rate profile for the workout may look like this: 181, 181, 183, 184, 186, and 188 beats/ min.
    As the athlete fatigues, the heart must compensate by beating faster to pump enough oxygen to the working muscles. The heart rate profile during the workout can help the coach determine when fitness gains have taken place. For example, say this athlete runs the same workout-6 x 800 meters-two months later, and the heart rate profile looks like this: 179, 179, 180, 180, 182, and 183 beats/ min. Assuming all else being equal (temperature, wind conditions, fatigue level), you could say that this athlete has improved his fitness.
    Using the information in the table, a sample training week during the early competitive phase for a 5,000-meter runner could look like this:
Monday:

2 miles warmup @ 70-75% max HR
5 x 1200 meters @ 95-100% max HR with equal time jog recovery
2 miles warmdown @ 75% max HR

Tuesday:

8 miles @ 70-75% max HR

Wednesday:

2 miles warmup @ 70-75% max HR

3-mile lactate threshold run @ 80-90% max HR

2 miles warmdown @ 70-75% max HR

Thursday:

Rest

Friday:

5 miles @ 70-75% max HR

Saturday:

Race

Sunday:

10 miles @ 70-75% max HR.

 

 

ENVIRONMENTAL CONDITIONS
    Where your athletes run greatly affects their heart rate responses to training. Running in the heat increases heart rate in order to increase peripheral blood flow to the skin to improve evaporative heat loss from the body, while running in the cold decreases heart rate in order to keep in the heat. Thus, running in the winter at 7:00 mile pace may elicit a HR of 130 beats/min., while running at that same pace in the summer may elicit a HR of 140 beats/min., even if your athlete is in better physical condition.
    The hotter the body gets in the heat, the more the heart rate will in- crease in an attempt to maintain core body temperature at a safe level. Therefore, when running for long periods of time in the heat, heart rate will drift upwards as the run continues. When acclimatized to the heat, however, training runs can be per- formed for longer periods of time before the heart rate changes to the extent observed before acclimatization.
    Running at altitude also presents an environmental stress to the distance runner, increasing his or her heart rate. The higher the altitude, the less amount of oxygen bound to hemoglobin (the carrier for oxygen in the blood), which results in less oxygen available to the muscle cells. Therefore, the heart has to beat more often to supply oxygen to the muscles.

    Again, once your athletes are acclimatized to the higher elevation, changes in heart rate will diminish compared to that observed before acclimatization, although it may never completely return to sea level values while at altitude. This acclimatized-induced drop in heart rate at a given intensity at altitude can thus be used as a time marker for acclimatization, and can signal to the coach when the athlete has gained the benefit of altitude training and when it is appropriate to return to sea level for competition.

HEART RATE MONITORS
    Until recently, determination of heart rate during training has been difficult due to the lack of measurement devices. Runners would have to stop in the middle of their run and count their pulse either in their radial or carotid arteries. Since heart rate drops rather quickly during a pause from an activity, especially in trained runners, this method does not give an accurate measure of the heart rate while running.
    Today, electrical heart rate monitors can accurately determine heart rate while running. The wireless monitor, which is simply worn around the chest and sends an electrical signal to a wristwatch, offers constant readings of heart rate throughout the duration of the workout. Although it can be expensive to purchase heart rate monitors for all your athletes, and wearing it may take some getting used to, both the time and the cost are worth the knowledge gained from using it.
    One of the best uses for heart rate monitors is to slow the pace of recovery runs enough so that your athletes sufficiently recover from the previous day's interval workout and are ready to handle another interval workout the next day. Thus, the heart rate monitor serves as an objective measure for the coach, allowing precise determination of the degree of effort.
    However, it is important to remember that, although heart rate at any given running intensity can reflect the physical working capacity of an athlete, there are limitations associated with using heart rate as a single dependent variable. Heart rate can vary apart from fitness level and is often related to emotional state, environmental conditions, amount of sleep, or elapsed time after a previous meal.
    A good idea for a coach would be to use heart rate monitors with all of their athletes and link their individual workout paces with their individual heart rates. The coach could also link suggested workout paces to his or her athletes' actual heart rate values. For example, Coach Jack Daniels has suggested specific paces for different workouts based on an athlete's race performance-determined VO2 max, which Daniels calls "VDOT" (Daniels, 1998). Using the athlete's VDOT paces, an entire heart rate profile can be generated for each athlete.
    Once this profile is established, the coach could specifically target his or her workouts for each athlete based upon what actually was a given runner's percentage of max HR at a specific pace at a specific time of the training year. Over months and years of training, pace changes for workouts can be matched with heart rate changes, making the measurement of fitness gains more objective and observable.
    Since high school and college coaches can typically monitor their athletes' training over four years, the knowledge gained from such a training system can be at least as valuable, if not more so, as any physiology laboratory research.
    Finally, by monitoring training using heart rate, over time your athletes will begin to understand what a given heart rate feels like. This is important because becoming more aware of their bodies and the link between their physiology and their perceived exertion is a vital step to- wards high athletic performance. At the very least, it gives them an appreciation for the wonderful adaptations of the runner's body.

REFERENCES

Boulay, M.R., Simoneau, I-A., Lortie, G., and Bouchard, C. (1997). Monitoring high-intensity endurance exercise with heart rate and thresholds. Medicine and Science in Sports and Exercise.29(1):125-132.
 

Daniels, I.T. (1998). Daniels' Running Formula. Champaign, IL: Human Kinetics.
 

Wenger, H.A. & Bell, G.I. (1986). The interactions of intensity, frequency, and duration of exercise training in altering cardiorespiratory fitness. Sports Medicine, 3:346-356.
 

Wilmore, I.H. & Costill, D.L. (1988). Training for Sport and Activity: The Physiological Basis of the Conditioning Process. Champaign, IL: Human Kinetics.

FROM: TRACK COACH 158

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