1. From a rack, place barbell behind head so that barbell is centered and lying on top of spine while hands grip the bar to stabilize 
2. Bend knees to 90˚, lean butt back, and maintain knees inside the shoulders (Knees should point same direction as feet throughout movement)
3. Keep back straight by keeping the head up, pushing chest out and shoulder blades up
4. Now, keep the weight on the heels and push gradually vertical through the heels by extending knees and hips until legs are straight
5. Return and repeat

Targeted Muscles

• Quadriceps
• Hamstring
• Glutes
• Calves  

Stance & Grip

• Feet are shoulder-width apart, toes pointing outwards 10 - 20˚  
• Handover grip, palms facing down; hands are outside shoulders

RECOMMENDED LINKS

• http://www.fit-2-hit.com - Blog on Athletic Conditioning & Health
• http://www.conditioning-coach.com  - Tennis & Conditioning Coach