Time to upgrade the routine. Just make a few more series, you can expect to earn much stronger, as evidenced by a study conducted in Australia.
After six weeks, the athletes performed eight sets of squats twice a week got a 20% increase in strength, while those who only made four series only managed a further 14%.
Start with a weight squats, bench or exercise deadweight. If you want something more daring provar try with kettlebells. The kettlebell swing can become a safe substitute squats.
When a group of British scientists analyzed barbell squats and movements with the kettlebell, found that such movements were worked intensively muscles. It also minimizes the possibility of injury.
Place your hips back and swing the dumbbell between your legs. Push your hips forward and drives the kettlebell to shoulder height. Do five sets of 30 seconds.