It's no secret that strength training is the single most effective way to build muscle (well, that and getting your fill of protein), but if you play your cards right, even your cardio routine can help you more quickly see those gains.
Corey Phelps, an NASM-certified personal trainer, recommends running intervals, in which you rotate between 30-second sprints and 30-second recovery periods for 10 to 20 minutes, to effectively build muscle while blasting fat. You might also try incline sprints on the treadmill or outside on some stairs. "The incline will target the quads, glutes, and hamstrings, and the sprints will activate core muscles," Corey told POPSUGAR. "Run up the steps as fast as you can. Propelling the body upward is tremendous work and creates a perfect environment for muscle growth."
If running isn't your speed, Corey also suggests rowing intervals, alternating between sprints and recovery reps to build muscle. (Try this 20-minute interval workout, keeping a close eye on your form.) "Rowing targets every muscle in the body, especially the glutes, hamstrings, and quads," she said. "The explosive power used to press off the footrests targets the lower-body muscles."
Of course, Corey noted that you can't blast away bad eating habits with cardio and strength workouts. When it comes to building muscle, a balanced diet focussed on adequate protein intake is key. Finally, don't be alarmed if you see the number on the scale increase slightly; muscle weighs more than fat, so this is actually normal. Instead, focus on how your clothes fit and watch for increased muscle definition. If you stay consistent, you'll slowly but surely start to see results.