Sunday, April 13, 2008

HRV, EPOC & Training Effect

This post includes an article written by Don Hagan, PhD. about the "Training Effect" system and Suunto t series monitors. Don was a good friend and wrote this summary a few months before he passed away in 2007. He will be missed.

New technologies are emerging allowing the athlete to better monitor the effectiveness of their exercise training program. It is now common to use a chest belt with electrodes to measure exercise heart rate to determine if one is getting a sufficient training stimulus, and for computer systems to store this information for further evaluation. However, heart rate is only part of the story. New research suggests that heart rate variability (HRV) and excess post-exercise oxygen consumption (EPOC), which is the amount of oxygen consumed after exercise during recovery, can be used to monitor the effectiveness of exercise sessions and training programs, and monitor fatigue and recovery.

Suunto of Finland has taken these advances and incorporated them into small wrist-top computers, called the “Suunto t6" (and recently added are the t3 & t4 monitors). Information captured in the wrist-top computer can be downloaded into a personal computer for further storage. In the Suunto t6 system, the athlete wears a chest belt containing electrodes which record heart beats. The heart beat signals are then transmitted to the wrist-top computer, where the time intervals between respective heart beats are measured and analyzed for fluctuations in the time intervals. The information also can be downloading to a PC and exercise sessions can be analyzed using a specialized Training Manager software program or transfered into online platforms like the Training Peaks TM Platform.

The major innovation of the Suunto t6 system is its capacity to measure heart beat time intervals and determination of HRV. Understanding the mechanisms controlling heart rate allows one to better understand the utility of the Suunto t6 system. Heart rate is regulated by both the parasympathetic and sympathetic nervous system, which work in an inverse, interactive fashion. That is, when one system is in control, the other is quiescent, and vice versa.

During rest, heart rate is primarily controlled by the parasympathetic system, and HRV occurs due to increases and decreases in chest size associated with the inspiration and expiration of breathing, respectively. During inspiration, the time difference between heart beats becomes shorter, which causes heart rate to increase slightly. Likewise, when one breaths air out of the lungs, the time difference between heart beats becomes longer, and heart rate decreases slightly.

During rest, the influence of breathing on HRV will force heart rate to vary by several beats above and below its average rate. The effect of breathing on HRV also is evident during light exercise up to a heart rate of about 110 bpm. However, movement from rest to light exercise, and then to moderate and heavy exercise, is associated with a gradual decreases in both parasympathetic control and HRV, and to an increase in sympathetic control of heart rate. At maximum heart rate, sympathetic control is nearly complete, while the contribution from the parasympathetic system is negligible.

Aerobic capacity and exercise training influence HRV. Chronic exercise training produces a decrease in resting heart rate, or bradycardia, due to enhanced parasympathetic control. As a result, endurance athletes have greater HRV than do non-endurance athletes at rest and during low-levels of exercise up to the ventilatory threshold. A healthy heart has a large HRV, while individuals with heart disease have less HRV. Evidence shows that people with low HRV have an increase risk of heart attack.

An important feature of the Suunto t6 is the use of HRV to estimate the level of EPOC required for an exercise session. Recent research evidence suggests that EPOC can be used to evaluate the effectiveness of an exercise training session and monitor fatigue. EPOC is related to the intensity and duration of the exercise work bout, i.e., the greater the intensity and the longer the duration of a training session, the greater the EPOC. Thus, a high intensity exercise session will have high EPOC, while low intensity exercise will have low EPOC. This is why it is impossible to train every day at one’s maximal oxygen uptake capacity. The post-exercise oxygen consumption requirement is so high; one is not able to pay off the debt before starting the next high-intensity exercise session. This also means that a training program with an emphasis on low-intensity, long duration exercise will produce lower EPOC, because the energy requirement of the exercise work bout is paid using atmospheric oxygen and not stored energy sources. A high EPOC without adequate rest and restoration will contribute to an athlete becoming “over trained” and more susceptible to injury.

In addition to measurements of heart rate, HRV, and estimation of EPOC, the Suunto t6 system has the capacity to estimate and record breathing rate and the pulmonary ventilation, or volume of air moving into and out of the lungs. Both of these measures can be of use in understanding the stress of an exercise work bout. For example, exercise intensities above the lactate threshold are characterized by a higher breathing rate and pulmonary ventilation than exercise below the lactate threshold. You know you are in this zone when talking to your exercise partner is difficult.

It is well known that heart rate at any given work rate is reduced as a result of training, and that decreases in exercise heart rate are an indicator of an increase in aerobic and endurance capacity. The same response occurs for breathing rate and pulmonary ventilation, which transfers into a lower energy cost of breathing during exercise, and improved work efficiency.
In the Suunto t6 system, heart rate and HRV are used to determine the stress of the exercise session and training stimulus by estimating EPOC associated with the exercise session. By monitoring EPOC, an athlete can follow their adaptation to training, and determine when to increase the exercise stress level to repeat the adaptive cycle.

An important feature of the Suunto t6 system is the Training Effect function in the Calendar View of the Training Manager software program. The Training Effect function displays the performance and exertion level of the exercise session based EPOC value. With this function, the athlete can follow successive performances and see their rate of adaptation. The function also allows the athlete to determine whether or not an “overreaching” or personal-best performance leads to overtraining.

Advances in biosensor and wireless technologies, and data storage and analysis software programs are allowing scientists, coaches, and athletes to better measure the responses of athletes to training and to develop a greater understanding of the adaptive process associated with exercise training. These developments will likely lead to improved personal performances, racing strategies and training regimens. The Suunto t6 is one of the leaders in this new trend of combining science and technology into new tools for the benefit of today’s athlete.
Don Hagan, PhD. has 25 years of experience conducting exercise physiology research and has published 60 manuscripts on a wide range of exercise training topics. Dr. Hagan’s previous research experience includes working as a researcher at the Cooper Institute for Aerobic Research, Institute for Human Fitness, University of North Texas Health Science Center, and Naval Health Research Center in San Diego. He is currently working for the Space and Life Sciences Directorate at the NASA/Johnson Space Center in Houston.

The information and programs are for informational purposes only. They do not substitute for the advice of a qualified health care professional or physician.

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