Weightlifting without a doubt increases your testosterone. After weight training consistently for about 8 months, there are definitely changes beyond muscle growth
But there's a problem, if your testosterone level is too low. In my experience, that increases the risk of tendonitis. Also, it didn't seem that exercise did much good. At least, not for strength training.
But with testosterone supplementation, exercising builds muscle and reduces fat. And no tendonitis. Also better blood sugar management, and less acne. Maybe even darker hair. But clearly not more hair on my head.
That's interesting you attribute low testosterone to tendonitis because high testosterone does the same thing. In fact, that's why steroids (testosterone ethanate) can increase the chance of injury in abusers because the muscle grows in strength far faster than the tendons so they tear. However, the benefits of testosterone supplementation vastly overweight the cons if you are naturally low and I suspect that it starts a positive re-enforcement cycle where increased testosterone increases muscle which then stimulates more testosterone production until a good equillibrium is met.
