Meet Dr. Z
Hi! I am Dr. Jim Ziegler, better known as Dr. Z. I have had a long career as a pediatric cardiologist. I didn’t learn much about exercise during my training, but when I moved to Rhode Island to work at Hasbro Children’s Hospital as an attending pediatric cardiologist, I taught myself exercise physiology and built a state-of-the-art pediatric cardiopulmonary lab. I have run that lab for the past 30 years. Over that time span, I have supervised and/or interpreted thousands of stress tests in children, teenagers, and young adults, some subjects healthy but with exercise-limiting symptoms, and some with cardiac problems, ranging from mild to severe. Some of those tests have been straightforward, done on a treadmill, gradually increasing speed and incline while monitoring heart rate, blood pressure, and electrocardiogram. Some have included pulmonary function testing if a concern for baseline or exercise-induced asthma has been raised. Some have been what are called metabolic stress tests. Metabolic stress testing precisely measures the integration of cardiac, pulmonary, circulatory, and muscle cell function.
For a metabolic stress test, the subject needs to gradually exercise to exhaustion while wearing a comfortable, form-fitting mask over the mouth and nose that measures ventilation (how much someone breaths), the amount of oxygen consumed, and the amount of carbon dioxide produced. The maximal amount of oxygen consumption, V̇O2 max, correlates very well with functional status. Along with V̇O2 max, other measured exercise parameters help guide therapeutic decision-making in “sick” individuals with cardiac problems.
But metabolic stress testing has applications outside of “sick” populations. It allows for measurement of numerous parameters, some directly and some indirectly. For individuals interested in optimizing wellness, V̇O2 max is the single best marker for predicting present health status, overall wellness, lifespan, health-span, and freedom from death and chronic disease. If low, increasing one’s V̇O2 max has powerful positive health consequences. In athletes, V̇O2 max correlates well with endurance potential or what is called maximal aerobic power. Maximal aerobic power predicts performance. Almost as important, metabolic stress testing allows for measurement of fuel utilization (fat versus carbohydrate), calories burned, the precise breakdown of heart rate zones, and when the body “switches” from mostly aerobic to anaerobic metabolism. Beyond the switch point (the anaerobic threshold), it is difficult to sustain exercise intensity for more than a short period of time because of the build-up of lactic acid. So, for an endurance athlete, the higher the V̇O2 max and anaerobic threshold, the greater the potential for high level performance. Training can be geared to increase these parameters.
As a pediatric cardiologist, lifetime runner, and exercise enthusiast, I find exercise physiology fascinating. Knowledge of one’s metabolic parameters allows for optimizing performance, fine-tuning training, and chasing one’s goals.
I truly believe that there is “strength in numbers,” and for that reason, I have built the first metabolic stress testing service available to the public at large in Rhode Island. I hope to assist individuals on their paths to better health, and endurance athletes, both recreational and competitive, striving to optimize performance and reach their potential.