I’m fit right? Many people who are physically fit believe they can cross over into another sport and their fitness should translate. This may be true to some extend, but if the sports are different enough, things do not translate.
There are multiple aspect of fitness that make you a strong runner (or strong any other type of athlete. Aerobic fitness is the stimulation and strengthening of the heart and lungs, which improves the bodies ability to transform oxygen you breath in to energy your muscles can use. Having enough oxygen throughout your body is critical to participating in endurance events, okay and life.
Aerobic fitness is important but it’s not enough if you want to be a strong athlete in a particular sport. Strength in the muscles specific to the sport does not always crossover and complete crossover is pretty much impossible. You can compare muscle development between athletes of different sports to see proof, unless they make special effort to achieve more balanced strength. Runners have more balanced development throughout the legs. Sometimes the calves and quads can be more developed. Cyclists typically have larger quads, specifically the one on the outside. Swimmers have larger shoulders and arms. Those who play team sports requiring a lot of lateral movement are going to have stronger supporting muscles in the legs and core.
Running uses every muscle in your body as to most other sports. The difference is in the role each plays and the level of reliance on that particular muscle group. The major muscles of the legs are the most used in running. There are smaller, support, muscles in the legs used as well. At times these support muscles are recruited to pull more of the load than normal when the big boys become fatigued or injured. Even within the running community there are going to be differences in leg development because of the training each runner does.
Muscles and tendons remember. Neuro-pathways or muscle memory develops with experience. Your body becomes more efficient in form. When you repeat a motion over and over again, it becomes ingrained and you don’t have to put much, if any, thought into it. The less you have to think about each movement the faster you will become. The reduced attention required allows you to focus on one aspect of your body and make tweaks here and there to improve your form reducing injury and energy consumption. For runners, leg turn over, cadence, and stride length are all improved by building neuro-pathways. In contrast, soccer and American football players have unmatched agility (foot movement) because they work on it day in and day out.
The range of motion required by your muscles is different for different sports and on the other side the muscles and tendons which tend to tighten up are different depending on your sport. Flexibility in the hamstrings and hip flexors is important for running because they control the movement of your leg swing. Flexibility in those muscles is not as important for swimming or rowing.
Bottom line here is don’t get frustrated when you really struggle when cross training or picking up another sport. Fitness encompasses many aspects and unless you make an effort to maintain balance across these you’re not going to be at the same level in each sport. Individual strengths also separate athletes in the same sports.