I am a 5k runner. 48 years of age. Been lifting now for over a year and a half. I am specifically doing Olympic lifting.
Started out unable to squat body weight of 150 lbs and now have a pr in front squat( full squat- butt to calves) of 102.5 Kilo or 225 lbs and 100k for back that is 1.5 times body weight.
My concern starting was acquiring unwanted mass. This has just not happened.
This is what I have found. My speed has improved like nothing else. I am faster now as a 48 year old then I was in my 20s. Just ran easy 6 seconds 50 meters. This is something I could never have done.
My posture and bio mechanics have significantly improved, having a more erect posture and a more glute dominant stride.
Now as far as aerobic capacity, I have not found this mode of training to make a dent in that. This is specific to the type work done and getting stronger has not made a difference to my VO2 or Lactate balance point or lactate endurance, but others may find different.
My routine consists of 3 visits to the gym with a Olympic Wt coach and sometimes add days other than that, but typically 3 days per week. Routine includes squats( Front- back), squat and power cleans/ snatches as well as other components specific to the snatch and clean and jerk. e.g. press work, pulls( dead lifts), cleans from the hang or off blocks, etc.
Beside technique,that involves low weight, my major strength lift( the squat) are low rep, usually now start with 60K for 5 followed by progressions of 3-70, 2-80, 1-85 and up.
Reps won't get me strong, but working at or above 80 percent of 1 rep max will. I was stuck until I learned that heavy weights require neurological requirement that can only come by testing my max. Failure is part of the process, but not a routine.
Have found it best to have de- load weeks, in that I might continue to squat with 60- 70 percent easy weights. Sometimes a week total break has been great for my motivation and strength.
All in all, I see major benefits from the work I have done. I feel good doing it and have learned to apply the mental aspects of weightlifting to running, that is a great asset.
Again, weights haven't made me aerobically superior, but I now have the framework, the core strength and enhanced movement abilities to develop this specifically by the work I know generally works, e.g. threshold and above+ endurance.