Strength training or resistance training is the use of resistance to muscular contraction to build the strength, aerobic endurance and size of skeletal muscles. A well-rounded fitness program includes strength training to improve bone joint function, bone density, muscle, tendon and ligament strength, as well as aerobic exercise to improve your heart and lung fitness, flexibility and balance exercises. The Australian physical activity and sedentary behavior guidelines recommend that adults do muscle strengthening activities on at least two days each week. Strength training programs should be monitored and changed every 6-8 weeks to ensure continued improvement. Variety of exercise, reps and sets should be adopted to ensure the body is continually challenged.