Try dropping the spinning class and doing 2 leg sessions a week. Low/No weight
E.g - Leg extensions, 20 reps, 3 sets. Squats (In the smith), 20 reps, 3 sets. Leg Press, 20 reps, 3 sets. Leg extensions - AGAIN, 20 reps, 3 sets
If you are walking afterwards add a little more weight.
Vary you...