Understanding Heart Rate Assessments

understanding-heart-rate-assessments-cardio-fitness-educationMeasuring and  recording heart rate data is essential to the  HZE program. In fact,  without accurate data, developing a training plan  is not  possible. Students may  use  a number of different assessments to develop their training plans, each of which is valuable in and  of itself. When combined and compared with others, these assessments can show  trends and starting points, which students can then use to make healthy exercise decisions. This is the power of a heart monitor: it helps students make health and  fitness decisions.

Resting Heart Rate

Heart rate changes with the  time of day, increasing during the  daylight hours and decreasing during the  night  hours. Resting  heart  rate is the  heart rate first  thing  in the  morning, before getting out of bed. Because it measures parasympathetic nervous response, resting heart rate is one of the  key indicators of overtraining or other stress.

Resting heart rate, sometimes referred to  as  a.m.  heart rate, decreases as  a result of positive training activities, meaning that as you get fitter, your  heart works  less  to do the same work. A lower  resting heart rate means less physiological stress on the  heart muscle because it contracts fewer  times. Although heart rate escalates dramatically during a training session, fitness training results in a lower  resting heart rate, which translates to fewer contractions over  the course of a lifetime. In other words, the heart of someone who exercises has  to  work  less  over  that person’s lifetime. This  is one  of the  training  effect responses. The result of this  training effect is that a person can save  more than 700 million heartbeats over the course of a lifetime  (learn more about this  in appendix B). That’s quite a payoff in the  long run.

Ambient Heart Rate

Ambient  heart  rate is frequently confused with  resting heart rate. Ambient heart rate is measured when  the  person is awake  but  sedentary—for example, when  resting in a sitting position while awake  and  involved in a sedentary activity such as working  on a computer, watching television, or talking. Resting heart rate, on the other hand, is taken in bed before rising  when  the  heart is at complete rest. Ambient heart rates change as a result of stimuli that influence heart rate including body  position; external influences such as temperature, hydration, and  food  ingested; internal influences such as  level  of fatigue, stress, hunger, and  sleep; and  medication.

Ambient, or sitting, heart rate, like most heart measurements, is relative, not absolute. It is a number that needs to be compared to other ambient heart rate measurements. Taking ambient heart rates repeatedly gives a more accurate assessment than measuring it once. The  normal range for ambient heart rate is usually between 50 and  90 bpm,  but  healthy ranges of ambient heart rates are  very  broad. The  training effect  is also  seen in ambient heart rates. In other words, the  fitter  you become, the  lower  your  ambient heart rate will be.  Ambient heart rates under 60 bpm  are  rare. An ambient heart rate over  80 bpm  may indicate a combination of various types of stress.

Delta Heart Rate

The  famous poet David  Whyte  once wrote, “All things change when  we do.”  That’s the principle behind the  delta heart rate assessment. Delta (Δ), a letter in the  Greek alphabet, means “change.” Hence  the  delta  heart rate, or orthostatic heart rate, is a measure of the heart’s response to a change in body  position.

Heart rate alters with  changes in body  position. Its increase and  decrease depends on the workload demand on the heart muscle. If you lie down,  for example, your heart doesn’t have  to work  as hard as it does when  you  are  standing because it doesn’t have  to pump blood upward against the  force  of gravity. Likewise,  a sitting position elicits a lower  heart rate measurement than the  standing position.

Stress can  also  affect  heart rate. Thus,  delta heart rate can  be used as an indicator of current stress. If you are overtraining, are on the verge of a respiratory infection, are suffering from a lack of sleep, or have  recently changed your  diet,  for example, your  delta heart rate will be higher than normal. Competitive athletes commonly use delta heart rate as an indicator of overtraining or pending immune compromise.

The most common way to measure delta heart rate is to record the heart rate when lying down and then when standing. The difference (standing heart rate minus sitting heart rate) is the delta heart rate. The change in heart rate values results when  the  heart responds to  different workloads. Because a healthy heart can adjust efficiently to small  changes in work load,  a higher delta heart rate might  indicate a less  fit cardio vascular system. However, it could also  indicate stress from internal or external conditions. Once  a person has  recorded multiple readings, the delta heart rate measure can be used as an indicator of cardiovascular fitness or stress. In a lying position, the  heart rate lowers to a value  close to resting heart rate (figure  2.2, P).

When  we  stand up,  the cardiac system adjusts to this change in body  position: the  heart rate increases and  then drops. Eventually, usually after  about two minutes, the  heart rate hovers around a new value  (figure  2.2, S). The change in heart rate, known as delta heart rate, is the difference between P and  S. In figure  2.2, for example, the  delta heart rate is 15 bpm  (85 – 70 = 15).

taking-your-pulse-cardio-fitness-2

Figure 2.2    Delta heart rate test

Recovery Heart Rate

Recovery heart rate measures the heart’s ability to return to its normal rate after exercise. It is a trainable heart rate, meaning that the  more fit one  becomes, the  more quickly  the heart rate returns to preexercise rates once exercise is stopped. Recovery heart rate is the time between the cessation of exercise and the heart rate’s return to its preexercise level. A common recovery heart rate measurement is one to two minutes, although total recovery may require as long as an hour. The shorter the heart rate recovery is, the fitter  the person is. There are  two  types of recovery heart rate measurements: intrarecovery heart rate (within a workout) and  interrecovery heart rate (between workouts):

  • Intrarecovery heart rate is the time it takes for  the  heart to  recover within one workout session.
  • Interrecovery heart rate is the time it takes for the heart and specific muscle groups to completely recover between workout sessions.

Ideally,  students’ intrarecovery heart rates recover (i.e.,  return toward ambient heart rate) very  quickly. Some  call  the  interrecovery heart rate the  one  that falls like a stone; that’s how  quickly  it usually recovers. Interrecovery heart rates that are  slow  to recover can indicate a less-fit cardiovascular system or be a warning of heart-related conditions.

With conditioning and  the  use  of mindful  recovery, students can learn to improve their recovery heart rates. In fact,  to some extent, they  can  learn to consciously regulate their heart rates. Mindful recovery is also  an excellent tool for managing stressful situations.

Mindful  recovery involves the  use  of visualization, deep breathing, body  positioning, and  similar relaxation techniques to purposefully lower  the  heart rate as rapidly as possible.  With practice, students can  develop their own  relaxation strategies. There are  two methods of mindful  recovery:

  • Active recovery, which involves continuing to move gently
  • Passive recovery, which involves stopping all exercise

Maximal Heart Rate

Maximal heart rate (MHR) is the  maximal number of times a heart can beat in one minute. The heart will only contract so fast—and not  one  beat faster—that’s why it’s called MHR. MHR is a fixed value,  but  everyone’s MHR is unique. Two 17-year-olds could have  a difference in MHR as great as 40 bpm.

Measuring MHR is essential to HZE. It is the  base, or anchor point, for setting zones and the  core piece of information necessary for students to complete the  HZE course.

Physical educators often  teach their students the  age-adjusted MHR formula, 220 – age (also known  as  the  regression formula). This  equation was  developed in the  early  1970s by scientists Fox, Naughton, and  Haskell,  who  intended it to be only  a rough formulation and not representative of an entire population. In 1992, Dr. Sam Fox, director of preventive cardiology programs at Georgetown University Medical  Center, made this  statement in a Chicago-Sun Times  article: “The crude formulas that I am partly responsible for . . . are only crude first cuts” (February 2, 1992, p. 29). He developed the calculations with an associate, William L. Haskell, then a professor of medicine at Stanford University School  of Medicine. Although the formula has become widely accepted, there are no clinical  trials to support it and no published record of research to support it. Furthermore, in the sample, all subjects were male and under 55 years of age. Research has shown that people of the same age have widely varying MHRs, as much as 11 beats per  minute, and that MHR in fit people changes very little as they  age.

What We Know About Maximal Heart Rate

Maximal heart rate is a specific value: the maximal number of times the heart can contract in one  minute. As a teacher, you need to know and  explain to your  students the  following facts  about MHR:

  • It is genetically determined—that is, you are born with it.
  • It is a fixed (absolute) number that does not decline with age unless you become unfit.
  • It cannot be increased by training.
  • It is not an indicator of current fitness.
  • In young children, it is often measured at over  200 bpm.
  • It tends to be higher in women than in men.
  • It is affected by drugs.
  • It is not fully developed until after puberty.
  • It is not a predictor of athletic performance.
  • It varies greatly among people of the same age.
  • For most people, it cannot be accurately predicted by any mathematical formula.
  • It does not vary from day to day, but it is test-day sensitive based on physical impacts that day, such as drugs or illness.
  • Testing should be conducted multiple times to determine the correct number.
  • It is sport specific.
  • It is the basis for setting personal heart zones.

Measuring Maximal Heart Rate

Maximal  heart rate is the  best index  to  use  in setting individual heart zones. Because it serves as the  principal marker for exercise intensity, your  students will anchor their heart zones around MHR.

There are a number of approaches to measuring this value. Fit people, under the supervision of a qualified instructor, sometimes undergo a maximal heart rate test, which involves exercising to the point of fatigue in two to four minutes to determine their true MHR number. Exercise intensity is increased regularly until the person cannot continue. In this  program, however, students will take a series of submaximal heart rate tests and undergo an assessment below  maximal effort,  and  then use the  results to predict MHR.

MHR is sport specific. It is affected by factors such as the  type  and  amount of muscle used, body  position, and  environment (e.g., water versus land). Following  are  some of the factors involved in determining the  specific maximal heart rate for various sports:

  • Body position
  • Size and number of muscle groups involved in the activity
  • Ambient temperature of the environment
  • Type of activity, such as weight-bearing sports (e.g., running)
  • Use of equipment (e.g., wheels in cycling).

Some  of the  lowest MHRs are  recorded for swimming (a sport in the  prone position), activities done in colder ambient temperatures, and  activities that use  the  smaller upperbody  muscle groups. The  highest MHRs are  recorded for weight-bearing activities (e.g., cross-country skiing),  activities that use  the  large  muscles of the  body, and  activities that use both the upper and lower-body muscle groups. People who work out in multiple sports need to determine their MHR for each because it varies by sport. However, the HZE program uses a global, all-sport MHR to set zones, which is easier for teachers and students to follow. A global MHR is accurate enough to use for all sport disciplines in the school environment.

Testing for Maximal Heart Rate

The submaximal heart rate assessments used during the  HZE program are  the  1-mile (1.6 km) walking test, talk test, biggest number test, step test, and chair test. The mathematical MHR formula has  limitations and  is less  reliable than submaximal assessments.

Most  methods used to  determine MHR are  valued or  rated according to  the  ultimate use  of the  number obtained. Competitive athletes, for example, need very accurate numbers. The intention of the HZE program is to teach students the process for determining MHR. The numbers they get will be only estimates, and depending on  the  method used, the  estimated MHR will vary.  In the school setting, we are looking for a general all-sport maximum: a global  fitness estimate, not a specific MHR for each sport activity.

MHR can  be determined by exercising to a maximal intensity or by completing submaximal heart rate tests to estimate it. The most accurate method is a maximal test to near exhaustion, but  this  may  not  be practical in school settings and  is difficult  to do, particularly for the  unfit.  Thus,  exercise scientists have  developed a series of submaximal heart rate tests that can  be used to predict MHR. These tests most often  use  a formula that predicts MHR based on age. The theory behind this formula for predicting MHR is that the maximal number of times our hearts can beat decreases as we age.

The original studies on MHR were  conducted in the 1930s on fit young men and not fit older men. The results of those original studies are now being challenged. Several long-term studies of fit people indicate that MHR is related not  to age, as many  have  believed for so long, but  to lifestyle. For example, an active 30-year-old may have  an  MHR of 210 bpm.  If, as  that person ages,  she simultaneously decreases physical activity and  becomes sedentary, her  MHR will likely decrease. If, however, she were to exercise at a moderate intensity regularly as she aged, her MHR would likely remain unchanged. Indeed, Dr. Dave Costill (1996) conducted studies that follow the  same fit people over  a period of 22 years. His findings show  that MHR remained unchanged when  his subjects exercised regularly at moderate intensity.

People who  want  to  get  fit may  find  that exercising at  certain percentages of true or predicted MHR provides a variety of benefits, such as the  following:

  • Enhanced fat burning: Burning more fat and more total calories by training in different heart zones.
  • Improved stamina: Going farther, faster, and longer because endurance fitness improves (called improved endurance capacity).
  • Increased efficiency: Going farther on each calorie burned.
  • Cardiovascular improvement: Transporting nutrients and oxygen  throughout the body  more efficiently.
  • Psychological power: Increased alertness, mental stamina, and self-esteem.

At lower  exercise intensities (i.e., lower  heart zones), these benefits result in lowered blood pressure, reduced stress, and  stabilized body  weight. As the  intensity of a workout increases (i.e., higher heart zones), the  benefits of exercising change.

Leave a Reply