You’re going to get a mixed bag of answers/opinions because the research is inconclusive, at best, when it comes to endurance athletes and the benefit of strength training.
Your volume of strength training is dependent on your strength training goal. Big difference between improvements for health/general fitness and sport-specific performance. Can it be sport-specific? Yes, but it can be very complex, and often the juice isn’t worth the squeeze for most endurance athletes to sift through the google-sphere of worthless programming.
After a first year or training strictly s/b/r
As others have said, you should focus on the specific adaptations that only increased volume of s/b/r can produce.
If you’re going to lift for the health and fitness benefit, do a lower body push/pull weekly, and an upper body push/pull weekly, with 4-6 sets of 4-6 reps and a total of 4 exercises. This volume should only take @ 15-20 minutes each session at the most including w/u. Any more and you’re potentially wasting even more time from the s/b/r. Don’t get wrapped around the axle with circuits, trendy rep schemes, or name-brand approaches. Moderate weight, couple times weekly, for the benefit of health and fitness. Nothing frantic. Nothing that requires a primal scream heard from the locker room. Just a realistic approach to the limitations and benefits of strength training.
Ex:
Day 1
Barbell rear lunge, 4 x 4
Barbell military press 4 x 4
(Perform a set of each with no rest between exercises, and a 1-2min recovery between series)
Day 2
Romanian DL, 4 x 4
Weighted pull up 4 x 4
(Perform a set of each with no rest between exercises, and a 1-2min recovery between series)
Weight for each set should be a challenge, but don’t go to failure…the fatigue will detract from the s/b/r. And for the love of god, don’t think that you need more protein or to take in a protein drink after a workout like this. Go with water and carry on.
From what I can find online, unless the ST experts tell me otherwise, total body circuits seem to be the best
I’m by no means the expert, but this is not true. Do circuits work? Sure…but they are far from the best. Likewise, what I wrote above is not “the best.” Use strength training for what it is designed for.