Whether cardio exercise leads to muscle loss depends on the type of cardio, intensity, how it's combined with strength training, calorie intake, and individual body type, according to the health website Verywellfit (USA).
Proper cardio exercises can be very effective in reducing fat.
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Physiologically, muscle loss occurs when the rate of muscle protein breakdown exceeds the rate of muscle protein synthesis over an extended period. Cardio itself does not directly cause muscle loss. However, under certain conditions, cardio can contribute to conditions that are detrimental to muscle maintenance or growth.
Review studies indicate that prolonged, high-intensity endurance training, especially when combined with a large calorie deficit, can easily lead to muscle loss. The body will also be subjected to prolonged energy depletion and stress.
Additionally, the type of cardio greatly influences the risk of muscle loss. In fact, not all forms of cardio have the same impact on muscles. Low-to-moderate intensity cardio has less impact on muscle growth. Examples of such exercises include walking, brisk walking, and gentle cycling.
High-intensity interval training (HIIT) cardio strongly activates the nervous system and hormones, and generally has less impact on muscle mass than sustained-release cardio. In fact, HIIT can even help maintain muscle mass during fat loss. The type of cardio most likely to cause muscle loss is sustained-release endurance cardio, such as long-distance running for many hours each week.
Appropriate cardio does not cause muscle loss.
Therefore, many experts emphasize that proper cardio does not cause muscle loss and may even help reduce fat if done with the right intensity and duration. A prolonged calorie deficit is the main culprit.
Because of high cardio but insufficient calorie intake, the body needs to mobilize muscle protein as an energy source, especially when glycogen stores are low. To avoid muscle loss, many studies on protein metabolism show that consuming 1.6-2.2 grams of protein per kilogram of body weight per day helps maintain muscle protein synthesis even during high cardio workouts. The daily protein intake should be evenly distributed across meals.
Additionally, during a workout, whether cardio is done before or after weight training can also affect the effectiveness of the training. Cardio before weight training will reduce strength in lifting exercises due to nerve and muscle fatigue. This makes it difficult for the workout to reach the muscle stimulation threshold for growth. Cardio after weight training or on a different day helps to mitigate this, according to Verywellfit .