Low-impact cardiovascular exercise has traditionally been viewed as the gentlest of workouts, the domain of the mall-walking senior citizen. This misconception is corrected when assessed from a physiological point of view; low-impact exercise and low-intensity activities are entirely different physical concepts.
The amount and the duration of the impact directed into the muscles or the joints of an athlete are a function of the force sustained by the body during the activity. Sports such as basketball, with its running and jumping, or rugby, with its physical play, are by definition sports that are high-impact activities. Running, with its repetitive generation of forces directed into the joints, is also a high-impact endeavor.
Low-impact exercise may be of reduced intensity, but the two expressions are not synonymous. Impact is the degree to which the body is subject to the force of the exercise; intensity is the measure of how hard the body must work to perform the exercise. Intensity will include the output of the cardiovascular system, the anaerobic and aerobic energy systems, and muscular activity, all of which may be at a high level without stressful impacts being directed into the musculoskeletal system. There are a number of low-impact cardiovascular exercises that may be performed at any level of intensity. These workouts include various strength and stretching routines, walking, swimming, recreational cycling, crosscountry skiing, and aerobics-based programs such as cardio-boxing that do not involve contact or resistance elements.
Exercises that involve intense stretching and strengthening components are the quintessential low-impact activity. Many of the elements that comprise these activities are performed with the body placed in a stable and stationary position, with only the body weight of the athlete or the resistance created by stretching the particular musculoskeletal groups, which results in the application of a force on the body. Calisthenics, yoga, pilates, and aerobics routines where jumping and bounding components have been removed, are each a low-impact activity that is capable of being performed with great intensity for a significant workout interval.
Cardio-boxing is an aerobics workout offshoot that has become popular for its total body fitness benefits. In some cardio-boxing variations, the athlete is required to punch or deliver other blows to a heavy boxing training bag, a movement that creates a high degree of resistance, particularly to the arms and shoulders. In the cardio-boxing routines that involve intricate footwork routines, jumping rope, and various types of feinting and shadow boxing, the participant combines a low level of impact on the body with often high-intensity movement.
Walking can generate a significant amount of force through the impact on the physical structure, as the force of each stride moves through the foot, ankle, knee, and hip joints. For some individuals, their physical condition may result in further damage being caused through the absorption of these forces. For most persons, walking represents a low-impact exercise that may be performed at a gentle pace, or with an intense whole body motion, at speeds in excess of 5 mph (8 km/h); typical conventional walking is done at approximately 2.5-3 mph (4-5 km/h). This type of activity is sometimes referred to as power walking.
Swimming is a good example of an activity that is generally one of low physical impact on the entire body, and yet as intense as the participant wishes it to be. The energy required in swimming is significant; the body consumes more calories per hour in energy while swimming than it does in distance running, with additional concurrent demands placed upon the cardiovascular system and the respiratory system.
Cycling at a recreational, non-competitive level is also a low-impact pursuit. Such cycling will generally place the rider in the seat, a stable and consistent position for the entire activity; the stresses created by cycling are those generated in hard sprints or hill climbing. Mountain biking is an aspect of cycling that will tend to produce higher degrees of impact on the joints, due to the rougher riding surface. As with walking and swimming, the cyclist may work at a high level of cardiovascular intensity while placing more moderate stress on the musculoskeletal system.
In northern climates, cross-country skiing is a preferred low-impact cardiovascular workout. Unless the athlete is vigorously driving the ski poles into the snow surface to increase speed (sometimes referred to as a double poling technique) most of the body's joints move in a single direction, consistent with the skier's rhythm. The distance traveled, snow conditions, and degree of friction between the ski and the surface, the topography, and the fitness of the individual skier are all factors that determine the intensity level of the exercise.
Effective low-impact cardiovascular exercise should be capable of elevating the heart rate of the participant to a level greater than 50% of maximum. Low-impact cardiovascular exercises are inherently a low physical risk activity; they are effective for both the maintenance of general fitness as well as tools to assist rehabilitation.