Why: Isolating the muscles of the quads can be difficult without specific machinery, but by simply holding a dumbbell between your feet whilst siting on a box or a bench you’re able to work solely on ‘knee extension’, the primary function of the quadriceps.
High rep sets are a great finisher after squats and lunges for maximum growth.
How: Sit on a box or bench, with your back straight and a dumbbell between your feet. With your knees at a 90 degree angle, extend your legs so that they're straight and parallel with the ground. Ensure that the rest of the body remains stationary. Pause for a second before slowly lowering the weight back to the original position, ensuring that you do not go past the 90-degree angle limit.