gregf83 

That’s the heart of the question for which there isn’t a clear answer. If that hour in the gym is for core work to prevent or eliminate back or neck issues then it’s probably a good idea. If the 20hrs already includes a range of low and high intensity training then adding more high intensity training in the form of heavy lifting to build strength in your legs is likely to have a negative impact on the bike training.

The pros I follow are doing 25+ hrs/wk getting ready for the season now with plenty of tempo and threshold work. I see very little high intensity work on the bike and don’t imagine they can afford to smash their legs in the gym doing heavy squats. So if they can’t afford it while prepping for racing and they certainly wouldn’t want to be doing it in the middle of racing season when exactly would a good time be for adding in strength training targeted at the legs?

For the recreational cyclist doing 5-10 hrs/wk of low to moderate intensity then yes I think targeted strength training involving heavy lifting could be beneficial. Numerous studies have looked at this question and found a positive response. None of the studies I’ve seen have compared the effects of strength training in the gym with HIIT on the bike. I suspect the answer to that is far less clear. It’s like asking which set of intervals is optimal for improving performance? There isn’t a clear answer that works for everyone.

Personally, I prefer to do my high intensity work on the bike. If I want general fitness I’ve got a list of projects in my woodwork shop that all involve plenty of lifting for general fitness. I’m over 60 with about 10 yrs of power data. I can see where my high end has slowly declined. I suspect I could probably slow that decline doing 2 or 3 heavy lifting sessions a week but that would impact my riding and I prefer riding at this stage.