The question of when to perform cardiovascular exercise, often called cardio, does not have a single answer that fits everyone. Cardio is defined as any rhythmic activity engaging large muscle groups that elevates your heart rate and breathing for a sustained period. The optimal time depends on personal goals, daily schedule, and the body’s natural physiological rhythms. Understanding these factors helps place workouts strategically to maximize results and ensure long-term consistency.
Daily Timing: Morning Versus Evening
The debate between morning and evening cardio involves adherence and physiological outcomes dictated by the body’s circadian rhythm. Early morning exercise, especially before breakfast in a fasted state, increases the body’s reliance on stored fat for fuel. This fasting state enhances fat oxidation during the workout and potentially over the subsequent 24 hours. Completing cardio first thing in the morning also leads to better overall adherence, as it is less likely to be disrupted by later commitments.
Conversely, the late afternoon and early evening hours, typically between 3 p.m. and 6 p.m., often represent the peak window for physical performance. This timing aligns with the body’s natural peak in core temperature, which enhances muscle function, flexibility, and oxygen uptake efficiency. Exercising later in the day may also be preferable for individuals with cardiovascular concerns, as the morning surge of hormones like cortisol can temporarily elevate blood pressure. Ultimately, the most important factor is choosing a time you can consistently commit to, as routine is the primary driver of long-term success.
Contextual Timing: Sequencing Cardio with Strength Training
For individuals who combine cardio and resistance training, the order of exercises within a single session is governed by the “interference effect.” This effect refers to the compromise in strength and muscle gains that occurs when endurance training is paired closely with strength training. Intense cardio activates the AMPK signaling pathway, which promotes endurance adaptations but can inhibit the mTOR pathway responsible for muscle growth.
To maximize strength or muscle hypertrophy, it is recommended to perform cardio after strength training or separate the two by at least six hours. Starting with strength training ensures muscles are fresh, allowing for maximum force production and intensity during lifts, which is the primary stimulus for muscle growth. Performing high-intensity cardio first can pre-fatigue muscles and the nervous system, leading to a measurable reduction in lifting volume and power output. If both must be done in the same session, low-intensity steady-state cardio, such as walking, poses the least risk of interference.
Defining the “How Often” and “How Long”
The quantitative aspect of “when” involves meeting public health guidelines for frequency and duration to achieve health benefits. Adults are advised to accumulate 150 to 300 minutes of moderate-intensity aerobic activity per week, or 75 to 150 minutes of vigorous-intensity activity. A simple way to balance this is by equating one minute of vigorous activity to two minutes of moderate activity.
The relationship between intensity and duration is inverse; higher intensity requires less time to achieve the same health outcome. For example, a 20-minute high-intensity interval training session can be as effective as a longer moderate-intensity workout. Guidelines confirm that activity does not need to be continuous, meaning short bouts of exercise contribute toward the weekly total. Rest days are a necessary part of the schedule, allowing the body to repair muscle micro-tears, replenish energy stores, and prevent overtraining.