more on training for definition

this came in from a friend after my post yesterday:
I saw your post this morning about how to tone without adding muscle mass which made me reflect on my triathlon training over the last two seaons.

Last summer I was training primarily on olympic length triathlons (800 m swim, 24 mile bike, 10k run). The distance can take between 2-3 hours. My training included alot more what I would describe as quality or intense repeats. For example, 20 minute bike repeats at hr rate of 170-175 (my max is 195), and included more track repeats (800's-1,200's).

This year I focused on half ironman distance (5-6 hour race) which did include some quality, but mixed in with A LOT more distance (heart rate at 155-165; max). An example would be many more days of 12-15 mile runs at 7:45-8 minute mile pace (I have really slowed in my old age). Or, biking 90 minutes (including 30-40 minutes of hill repeats, followed by a 10 mile run at 7:30 pace).

The result is that I have a really great aerobic base, and can train literally all day long. However, it appears as if I am less cut and in poorer shape than last year. I know from my times that I am in better shape, but from appearance it seems otherwise. Why is this? I this simply age, or does intensity impact muscle tone?

this is my response:

Intensity impacts muscle tone. muscle tone comes from type II muscle fibers--they are larger and respond better to the intense training of repeats and intervals like you describe. type I fibers have higher mitochondrial content and use more oxygen therefore they are the ones trained during less intense, long-distance aerobic training, if training for tone, the downside is that type I fibers are smaller and not as quick to hypertrophy (get bigger) than the type IIs (actually they don't have the ability to hypertrophy like the type IIs)so the question for the training goal is: muscular definition or aerobic efficiency? if it is the former, then focus on doing the shorter distance tris--this will allow for more time efficient training as well; if you have the time and the masochistic tendencies, then stay with the 1/2 iron and longer distances.

increasing the intensity of training with high intense activities like plyometrics, sprint intervals, or power lifting with equipment like kettlebells and medicine balls will activate the type II muscle fibers responsible for definition. standard endurance training--like jogging for long periods of time or using light weights for numerous reps will train muscles how to use oxygen efficiently but type I fibers (oxygen using fibers) generally do not provide the muscle definition/tone that many people train for

so if you're looking to change your workouts to add more lean muscle, then increase the intensity and identify how you can either run for high-intensity intervals, or lift explosively (and safely) to stimulate type II fiber development

If you have a question, feel free to ask and if I don't know the answer, I'll just make it up