The Centers for Disease Control and Prevention (CDC), the ACSM, and the American Heart Association all recommend that individuals engage in strength training exercises at least two days per week.
According to the ACSM, a variety of exercises should be performed that work all muscle groups and can be performed up to three days per week (though there should be at least 48 hours between sessions). Most adults should perform two to four exercise ‘sets’ (a set is a specific number of exercise repetitions) per muscle group. Individuals should rest for two to three minutes between sets. The resistance or weight selected for each exercise should allow an individual to complete 8 to 12 repetitions per set, or the number needed to cause muscle fatigue but not exhaustion. This will improve strength and power for most adults. Older adults and/or those new to strength training may want to start with lower resistance and higher amounts of repetitions.
According to the ACSM, it is important to have specific goals to work toward (e.g., increasing muscle size, and/or improving muscle strength, power, and/or endurance). Each of these goals can be enhanced by modifying the load (or weight) lifted in a given set, the volume (or total number of exercises, repetitions and sets) performed in a given session, the rest period between sets, and the frequency or number of exercise sessions per week. The load, volume, rest periods, and frequency with which an individual performs strength training exercises should always be determined by his or her goals, fitness level, age, health, skills, interest, and convenience.