Impact is frequently confused with intensity, but the two are not synonymous. A high-intensity workout can be low impact, and vice versa. These definitions help clarify the difference, so you make smart training choices.
Impact: Describes the forces exerted on, and exerted by, the body. Impact is measured in terms of the emphasis on eccentric, concentric, and isometric muscle contractions.
Low impact: Exercise that minimizes absorption of eccentric forces and emphasizes concentric or isometric muscle contractions. This type of training can help you get and stay fit for the long haul, as well as keep you active and strong while recovering from an injury. Examples include swimming, cycling, pushing a weighted sled, using battle ropes, performing plank holds, and eccentric weight training.
High impact: Exercise that emphasizes eccentric contractions resulting from absorbing external forces. This powerful training can elicit a strong, adaptive, muscle-building response when paired with adequate recovery. When the body can’t recover, the wear and tear can be extreme. Examples include running, jumping, plyometrics, and the lowering phase of strength-training exercises, especially with heavy weight.
Intensity: How much effort a workout requires in terms of heart rate and oxygen expenditure. Intensity is measured as a percentage of your maximum heart rate, a marker reflecting how hard your body is working during an exercise.
Low intensity: If you have conducted an active metabolic assessment (AMA) and use a heart-rate monitor, low intensity means you are performing within heart-rate zone 1 to 2. On a rate of perceived exertion (RPE) scale (1 corresponding to very easy effort and 10 to very difficult), low intensity falls in the range of 1 to 3. Such a workout would allow you to easily maintain a conversation. Low-intensity training is commonly and beneficially performed in what is known as a “steady state,” in which the heart rate remains fairly low and stable. Called LISS — low intensity, steady state — this type of cardio includes a leisurely walk or bike ride.
High intensity: If you have completed an AMA and use a heart-rate monitor, high intensity means you are performing within zone 4 to 5. On an RPE scale, high intensity pushes you into 8 to 10. High-intensity training is popularly performed in an interval fashion known as HIIT (high-intensity interval training) because the rest intervals give you an opportunity to recover briefly in order to keep your intensity high during work intervals.