Research shows that some bodies react better to workouts than others.

A new study coming out of Finland indicates that some people’s bodies do not respond as expected to weight training, others don’t respond to endurance exercise and, in some cases, some don’t respond to either. In other words, this means that some people do not become fitter or stronger regardless of what kind of workouts they perform.

To reach this conclusion, the researchers enrolled 175 sedentary adults in a 21-week exercise program. Some lifted weights twice a week. Others jogged or walked. Some did both.

In the combined strength-and-endurance-exercise program, the volunteers’ physiological improvement ranged from a negative 8 percent (meaning they became 8 percent less fit) to a positive 42 percent. The results were similar in the groups that undertook only strength or only endurance training. Some improved their strength enormously, some not at all. Others became aerobically fitter but not stronger, while still others showed no improvements in either area.

Only a fortunate few became both fitter and more buff.

For More: New York Times