Your heart rate is the number of beats your heart takes in a minute. The average adult has a heart rate of anywhere between 60 and 100 beats per minute, or bpm. Factors that play a role in this wide variance in heart rate include age, body weight, body mass index and fitness level.
Body Size
Weight is often relative to body size, and body size can impact your heart rate. If you carry excess weight, your body tends to be larger in size. This means the heart must work that much harder to pump blood throughout the body. Your blood must move greater distances to reach your organs, muscles and other tissue. With the increased workload, your heart inevitably beats at a faster rate than the heart of someone smaller in size.
Evidence
A study conducted by the Division of Neurology at Deaconess Hospital in Boston showed a correlation between heart rate variability and overall body size. As weights and body mass indexes changed, the variability between maximum heart rate and resting heart rate did as well -- anywhere from 1.56 to 2.39 bpm. These results indicate that the poor health frequently associated with obesity is at least partly caused by the change in heart rate due to the increase in body size.
Fitness
Besides body size, excess weight is often proportionate to your fitness level. When you're overweight or obese, you're not only eating too much, but also exercising too little. Like any other muscle in the body, the heart grows stronger with exercise; therefore, leading a sedentary life can weaken the heart, requiring greater effort from the organ to move blood throughout the body. With the increased effort, your heart must beat faster to circulate the same amount of blood, elevating your heart rate.
Exercise
A study published by "Nutrition, Metabolism and Cardiovascular Diseases" demonstrated that body mass index, or BMI, which measures body fatness, affects both peak heart rate and heart rate recovery from exercise. The higher your BMI, the lower your peak heart rate tends to be during exercise, which means you're reaching your maximum heart rate with less intensity than you would with a lower BMI. Even if you're physically fit, yet carry excess body fat, your peak heart rate will be lower, negatively impacting your endurance. You won't necessarily be able to work out at a higher intensity for longer periods of time with the added weight.
References
- National Emergency Medicine Association: Heart Rate or Pulse
- Mayo Clinic; Heart Rate: What's Normal?; Edward R. Laskowski; Sept. 30, 2010
- "Nutrition, Metabolism and Cardiovascular Diseases"; Heart Rate Behavior During an Exercise Stress Test in Obese Patients; L.A. Gondoni, et al.; March 2009
- "American Journal of Cardiology"; Heart Rate Variability in Obesity and the Effect of Weight Loss; K. Karason, et al.; April 15, 1999
- "Clinical Autonomic Research"; The Relationship Between Heart Rate Variability and Measures of Body Habitus; R. Freeman, et al.; October 1995
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