I second what Coach Bob wrote. I do both and feel both are highly beneficial. Especially now: (1) Because I'm 65; and (2) Because I'm being treated for prostate cancer.
Obviously aerobic exercise is the foundation of cardiovascular health, which is the most important. And you can make a sound argument that swimming is the best form of aerobic exercise because it's (i) low impact, (ii) minimizes injury, and (iii) makes the most balanced use of all muscle groups. The last two factors are especially true when you swim the TI Way.
Additionally the American College of Sports Medicine recommends that for optimal health we do 3 sessions per week of aerobic exercise plus 2 sessions per week of resistance training. Resistance training can come in many forms, including many exercises that rely only on body weight and can easily be done at home.
Resistance training is important because, as we age, we naturally lose lean body mass. Even if our weight remains unchanged from 35 to 65 (fairly rare), we will still have quite a bit more fat and less muscle at 65 as a normal aging effect. The only way to counter this loss of muscle is resistance training.
I.E. Putting heavier loads on muscles than our (all-too-often sedentary) regular lifestyle does.
I prefer to do this with 3 or more weekly yoga classes, plus at least two sessions per week of weight training. I alternate one session with free weights and one session working on machines.
This is a great question. Watch for a blog on this topic in the near future.
Head Coach & Chief Executive Optimist
May your laps be as happy as mine.
My TI Story