Final answer:
Adults should engage in muscle-strengthening activities involving all major muscle groups on 2 or more days per week, according to the 2018 Physical Activity Guidelines for Americans. The correct option is (1).
Step-by-step explanation:
The recommendation for the frequency of resistance exercise according to the 2018 Physical Activity Guidelines for Americans issued by the Department of Health and Human Services is that adults should engage in muscle-strengthening activities on 2 or more days per week.
These activities, which should involve all major muscle groups, can include exercises such as push-ups, sit-ups, squats, and lifting weights. It is important to also recognize the need for rest and recovery, as overworking muscles can lead to delayed onset muscle soreness (DOMS), especially if exercise is extremely intense.
Therefore, a moderate exercise program of at least moderate intensity is recommended for muscle strengthening, and this can also contribute to a range of health benefits like improved cardiovascular and muscular fitness, increased bone density, weight maintenance, and cognitive function improvement.