As Commander mentioned, strength training is important and can be beneficial to increasing mitochondrial density. So starting each training session with a heavy compound movement then moving to another big exercise in a slightly higher rep range and then finishing with a high rep isolation exercise is the best way to go. And if you look at various programs, the best ones are always done this way to get the best of strength, size, and conditioning. So something like:
Barbell Back Squat - 3-5 sets of 3-5 reps
Barbell Front Squat - 3 sets of 8-10 reps
Machine Leg Curl - 3 sets of 15+ reps
That is just an example, you can obviously mix around exercises and use deadlift variations, leg press, leg extension, or whatever else based on your goals.
Also, high intensity interval training can increase mitochondrial density so you can do interval sprints on your off days.
"Strength is the product of struggle, you must do what others don't to achieve what others won't."
Squat: 463 Bench: 275 Deadlift: 518 Total: 1229
"Technique is always the first place to begin when striving to improve at a specific skill."
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