Why Running and Cycling Get Me Big Thighs


I am training for a race that involves a 20-mile run followed by a 30-mile bike ride. I’m petite and have always had little body fat – but since I started running and taking the occasional spinning class my legs and bottom appear to be growing bigger and bigger each week, while the rest of me is staying small and normal. Will this stop at some point as I can’t fit into any of my clothes!

Answered by Sarah Brown (A Fitness Expert)

Training for a 50-mile race is quite a task. It sounds like your body is responding to your training, but not in the way you prepared yourself for.

Adding muscle to your body is a good thing. Muscle makes you a strong athlete, and helps make your body more efficient at everyday tasks. Muscle also helps increase your metabolism (rate at which you burn calories). Females aren’t designed to build extremely large muscles, so by applying the right principles you can help them stay long and lean.

Everyone builds muscle differently, as we all have unique genetic makeups and different body types. While some people lack muscular definition, others can easily and sometimes rapidly gain muscle; similarly, some people have very little body fat, while others tend to carry a little more.

Running and cycling both require a great deal of lower body muscular endurance and power. When you train your muscles you create micro-tears; during your rest period your muscles repair themselves, becoming stronger and more defined. The greater the opposing force you put on your muscles, the more micro-tears you create and the stronger your muscles will become. If we apply this to cycling, the higher the gear you use (making it really hard to pedal) the bigger and stronger your muscles will become.

The best ways to ensure that your body does not build large ‘bulky’ muscles is as follows:

1. Stretch: Training shortens your muscle fibers and stretching helps lengthen them back out. Stretching each muscle group for 30 seconds to one minute after training helps return muscles to their pre-exercise length.

2. Lower intensity: Using a lower gear for a longer period of time will yield longer, leaner muscles than working in higher gears for shorter amounts of time. In preparing for a race it is necessary to train in higher gears to combat hills so don’t entirely skip this part of training.

3. Cross train: Cross training involves doing activities other than what you are training for (in this case cycling and running). Cross training helps develop your muscles to do other activities and improves your overall body strength, making you a more efficient athlete. Great cross training activities include swimming, rowing, jumping rope, weightlifting, yoga and pilates.

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