You can't train effectively for strength and endurance in the same exercise.
Muscles are made up of two major types of fibers. There are red, slow-twitch fibers used for endurance. And there are white, fast-twitch fibers used for strength and speed.
Endurance training converts fast-twitch strength/speed fibers to slow-twitch endurance fibers. This transformation can slow you down and reduce your overall strength.
Strength training reduces the part of the cell that produces energy for continuous movement. This change can limit how long you're able to exercise a muscle.
If you are a long-distance runner, exercising your legs against great resistance, such as working out on strength-training machines, may leave you too tired to maintain your regular running workouts.
If you are a competitive weightlifter, endurance training with both your arms and legs may limit your strength. Running long distances (which is exercise for both your arms and upper body) may interfere with strength gains.
Wrestlers, football and basketball players need to train for both strength and endurance.
Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition.