Long post, but it's a big topic.
I've been using weight training for various purposes for the past 45 years. When I started serious cycling training about 12 years ago, I began looking for a way to strength train which would complement the aerobic and anaerobic training from cycling. I've finally found a program that works for me.
If one is going to do any kind of training the first thing is to identify goals. My sole goal here is to improve my cycling. Cycling is basically about how many watts/pound one can produce at lactate threshold. A good sprint is also very helpful. One also needs endurance: how long one can ride at various power outputs. So for me, strength training will be in pursuit of these three things: LT power, sprint power, and endurance.
So let's have a look at this article, titled Effects of High-intensity Training on Performance and Physiology of Endurance Athletes, which is a compendium of many controlled studies:
It's definitely worth reading the whole thing. It's not that long. And guess what? High intensity intervals work very well. We knew that. But what sort of strength training produced gains on the bike? I'm going to look particularly at the studies by Bastiaans et al., which involved 4 sets of 30 reps, done explosively. If we look in the appendices, we find that intervals have by far the greatest effect on everything, except for 30 second sprints, where the explosive weights produced the greatest gains, 11% in 9 weeks. In all other tests where performance of Bastiaans' routines were measured, they did better than conventional weight training. My belief is that this strength program did so well because it is most similar to interval training.
So we see that if one has limited time, it's best to spend it on intervals rather than in the weight room, except for sprinting, where weight training can be king. 2 hour gym sessions aren't helpful. Why does high intensity training work so well?:
My investigation of applying strength training to cycling began with a program using 3 sets of 10, doing traditional weight training of various body parts on various days. I observed no effect. I then started doing 4 sets of 12 with a similar philosophy. I observed a small effect. Next I bought Friel's Cyclist's Training Bible and followed his weight training program for several years. I observed a considerable effect, but only early in the year when I was doing 3 sets of 30 as he prescribed. So then I started doing nothing but 3 sets of 30. That was better, but I was losing time for cycling and it was easy to overtrain. So I dropped back to 1 set of 30 and started doing that after cycling or other aerobic training. My performance took off. I no longer got dropped on the climbs and still won the sprints. Tweaking that program is where I am today. This is a form of high intensity strength training, which I believe offers specific gains for cyclists.
Some observations for which I don't have a citation: Training effect for cycling is maximized when muscle fibers are under tension for about 90 seconds. This means 3 seconds/rep for 30 reps, a nice pace and probably why I gravitated to this number of reps. Training effect is maximized when these reps are done to failure. In other words, you should fail just before reaching 30 reps and then do the last couple rest/pause or however you can. However, workouts done to failure should be spaced 3 days apart. If you can't do that, do one workout sub-failure and one to failure/week. Training effect is maximized when these reps are done after a mix of hard aerobic and anaerobic training, so after a hill ride, or a flat ride with sprints, or spin class. I believe this follows from the principle of pre-exhaustion, often used by bodybuilders before compound sets. I realize that, especially when starting this program, you will not be able to use as much weight after hard aerobic training as you could use if you were fresh. But using more weight is not the point. What you a trying to achieve is exhaustion. You'll be able to use more weight soon.
This is not the Bastiaans' workout. That happened to get studied, but I don't think it's optimal. Explosive movements can easily result in injury, take more time to reach the optimal 90 seconds under tension, and don't place the muscles under tension throughout the movement, only at the start of the movement.
This is kind of a crazy website, but it has some good information and is a good start for investigation of the issues around high intensity training:
Today, this is what I do, in order, one set of 30 each, no resting between exercises:
Leg sled: http://www.exrx.net/WeightExercises/...5LegPress.html
Seated rows: http://www.exrx.net/WeightExercises/...SeatedRow.html
Back extension: http://www.exrx.net/WeightExercises/...xtensionN.html
Barbell squats: http://www.exrx.net/WeightExercises/...s/BBSquat.html
Bench presses: http://www.exrx.net/WeightExercises/...enchPress.html
One legged calf raises: http://www.exrx.net/WeightExercises/...CalfRaise.html
Roman chair: more than 30 reps, no link
Total time: not more than 20 minutes.
OK folks, blast away! This program probably violates every principle of strength training you ever heard of. What can I say but "Try it!" Thanks for reading.