The Joy of Hill Sprints
Interval training on upwards gradients - better known as hill sprints - are great as they work just about every muscle in legs including your quads/hamstrings/calves/glutes and throw achilles tendons and hip flexors into the mix for a great all round lower body work out without having to lift weights (if you would like to run up hills with weights on your back then all I can say is much respect to you, just remember to build up slow though).
As well as a being a great substitute for leg day hill sprints are excellent for improving mental toughness and wind. I usually do 3 rounds of 3 sets of 3 minutes to work on my endurance, strength and aerobic conditioning. You can mix and match or use any one of these pacings individually to create a hill run routine.
ROUND 1 - 3 SETS FOCUSING ON ENDURANCE: 60-70% Steady pace up and down
IMPROVES STAMINA - Activates fat burning aerobic pathways and improves cardiovascular conditioning
ROUND 2 - 3 SETS FOCUSING ON ENDURANCE/STRENGTH: 70-85% Effort on the uphill active recovery (slow jog) on flat/downhill.
IMPROVES OVERALL PACE - Increases muscles' aerobic capacity - maximal ability to take in and process oxygen
ROUND 3 - 3 SETS FOCUSING ON STRENGTH: 85-100% Effort on the uphill brief stop followed by walking on the flat/ jog downhill.
IMPROVES MAXIMUM SPEED - Improves capacity volume of blood heart is able to pump. ADDED BENEFIT...depletes muscle stores of glucogen so body uses stored fat for after work out recovery, so all you have to do is sit back and shed those pounds