The high knees exercise is a dynamic, plyometric movement that mimics exaggerated running in place by rapidly lifting the knees toward the chest. This accessible, equipment-free exercise immediately elevates the heart rate, making it an effective form of cardiovascular conditioning. Whether high knees function primarily as an aerobic or anaerobic workout depends entirely on the speed and duration of the execution.
Defining Cardiovascular Exercise
Cardiovascular exercise, often shortened to “cardio,” is scientifically defined by the physiological demands it places on the heart, lungs, and circulatory system. An activity qualifies as cardiovascular when it sufficiently elevates the heart rate for a sustained period, typically targeting 50-85% of the maximum heart rate (MHR), generally estimated as 220 minus a person’s age.
A key measurement of cardiovascular fitness is the maximal oxygen uptake, or VO2 max, which represents the maximum amount of oxygen the body can consume during intense exercise. Consistent cardiovascular training enhances the efficiency of oxygen delivery, strengthening the heart’s stroke volume and improving VO2 max over time.
High Knees and Energy Pathways
The body relies on three interconnected energy systems to fuel muscle contraction, and high knees engage all of them depending on intensity and duration. The aerobic system, which is oxygen-dependent, is the primary producer of energy for sustained, lower-intensity activities lasting longer than a few minutes. This system uses carbohydrates and fats to continuously resynthesize adenosine triphosphate (ATP).
When high knees are performed at a maximum effort, the body quickly shifts to anaerobic energy production because oxygen cannot be delivered fast enough to meet the demand. The immediate, explosive bursts of knee lifts, lasting less than 10 seconds, rely on the phosphagen system, which uses stored creatine phosphate (CP) for rapid ATP production. For high-intensity efforts lasting between 30 seconds and three minutes, the anaerobic glycolysis system takes over, breaking down stored glucose without oxygen. This versatility means high knees can be programmed to train either aerobic endurance or anaerobic power.
Maximizing High Knees for Fitness Goals
High knees can be intentionally manipulated to target specific physiological adaptations, making the exercise adaptable for various fitness objectives.
Aerobic Endurance
To build cardiovascular endurance, perform the exercise at a moderate, sustainable pace. The focus is on duration, maintaining a steady pace for several minutes to keep the heart rate elevated within the aerobic zone.
Anaerobic Power (HIIT)
To maximize anaerobic power and intensity, integrate the exercise into a high-intensity interval training (HIIT) protocol. This involves performing high knees at a maximal pace for short bursts (typically 20 to 30 seconds), followed by a brief rest period. This style of training rapidly depletes anaerobic fuel stores, challenging the body to improve its capacity for explosive movements.
Proper Form
Proper form is necessary to ensure efficiency and safety. Engage the core muscles to stabilize the torso and maintain an upright posture. Drive the knees up toward hip level or higher, while maintaining a soft landing on the balls of the feet to reduce joint impact. Using the arms in a reciprocal running motion helps maintain momentum and increases overall intensity.