Save the rotation of your feet for open-chain moves like the leg extension, lying leg curl or single-joint calf exercises.
Behind the Blunder
Turing your toes in or out on exercises such as the leg extension, helps target the outer or inner quads, respectively. The same goes for the inner and outer part of the outer hamstrings, where you can shift the emphasis to different parts of the back of the leg when doing leg curls. However, those exercises are called open-chain movements, which means your feet are not pressed against a stable object. Never attempt to turn your feet inward of exercises where your feet are fixed, as in squats, leg presses or hack squats.
The key is to find a comfortable, balanced position where you can easily allow your feet to remain flat on the platform at all times, while letting yourself press through the heels and the balls of your feet for maximal power and strength. For most athletes, the foot position most comfortable is a toes-slightly outward stance.
Step inside a hack squat machine and place your shoulders and back against the pads. Place your feet narrow and low on the platform with your toes pointed out slightly, keeping your feet flat throughout the exercise. Maintain good posture, with your chest up and abs pulled in tight.
Unhook the safety bars and slowly yourself into the bottom position, stopping when your thighs are just beyond parallel to the foot platform. Pause, and then forcefully press yourself up to the start position, keeping your knees unlocked in the top position. Squeeze your legs and go right into the next rep.
Leg Remedy: Hack Squat Corrected
Keep your feet about hip-to-shoulder-width apart on the platform. Lower them slightly on the platform to shift more focus to the quads, specifically the vastus lateralis (outer quads). When you point your toes out slightly, you keep your knees, hips and ankles in a comfortable, safe and strong position from which to push.