Cardiovascular exercise, or cardio, is an essential component of a balanced fitness routine. Whether your goal is to lose weight, improve heart health, or enhance athletic performance, the timing of your cardio sessions can significantly influence your results.
This article explores the science behind when you should do cardio for maximum effectiveness, addressing variables like fat loss, energy levels, and workout performance, while citing reliable research to back up every claim.
Factors That Influence the Best Time for Cardio
Circadian Rhythms and Performance
The human body operates on a circadian rhythm—a 24-hour internal clock that influences energy levels, hormone production, and body temperature. Research has shown that exercise performance often aligns with these rhythms.
A study published in the Journal of Strength and Conditioning Research found that strength and endurance levels are higher in the late afternoon due to peak body temperature and improved neuromuscular efficiency (Chtourou & Souissi, 2012). While this might not directly apply to all cardio goals, it highlights the physiological advantages of exercising later in the day.
Hormonal Fluctuations
Hormones such as cortisol and testosterone fluctuate throughout the day and can impact your cardio performance. Cortisol, a stress hormone that promotes fat metabolism, is highest in the early morning (Kudielka & Kirschbaum, 2005). This makes morning cardio advantageous for fat loss, as higher cortisol levels can help mobilise fat stores.
Conversely, testosterone levels peak in the morning and gradually decline throughout the day. Testosterone supports muscle repair and growth, which can indirectly affect your ability to recover from cardio sessions.
Energy Levels and Nutrition
Your energy levels, influenced by factors like sleep and food intake, play a significant role in cardio performance. Morning cardio is often performed in a fasted state, which some studies suggest may enhance fat oxidation (Schoenfeld, Aragon & Krieger, 2014). However, fasted cardio might not be suitable for high-intensity sessions, as glycogen levels are typically lower after an overnight fast. For optimal energy and performance, cardio later in the day allows for more opportunities to consume meals and replenish glycogen stores.
Cardio Timing for Specific Goals
Cardio for Fat Loss
Fasted cardio in the morning is a popular method for fat loss. The theory is that low glycogen levels after an overnight fast force the body to utilise fat for fuel. A study published in The British Journal of Nutrition supports this, indicating that fasted cardio increases fat oxidation compared to fed-state exercise (Gonzalez et al., 2013). However, the total calorie deficit over 24 hours remains the primary driver of fat loss. If you prefer exercising later in the day, ensure you maintain a caloric deficit through diet and consistent training.
Cardio for Performance
If improving performance is your priority, the late afternoon or early evening may be the best time for cardio. Research in the Journal of Sports Sciences indicates that muscle strength, flexibility, and aerobic capacity peak between 4 p.m. and 8 p.m., coinciding with elevated body temperature and neuromuscular efficiency (Atkinson & Reilly, 1996). These physiological advantages make it easier to sustain high-intensity workouts, such as interval training or sprints, during these hours.
Cardio for Heart Health
For individuals prioritising heart health, consistency is more important than timing. However, studies suggest that exercising in the morning can reduce blood pressure and improve heart rate variability throughout the day (Jones et al., 2019). This makes morning cardio an excellent choice for those managing cardiovascular risk factors.
Morning vs Evening Cardio: Pros and Cons
Morning Cardio
Pros:
- May enhance fat oxidation due to elevated cortisol levels and fasted state (Gonzalez et al., 2013).
- Improves adherence to routines, as morning workouts are less likely to be interrupted by daily responsibilities.
- Boosts mood and productivity by releasing endorphins early in the day.
Cons:
- Lower body temperature and stiffness in the morning can reduce performance.
- Glycogen stores are depleted, potentially limiting high-intensity efforts.
- Early workouts may disrupt sleep if done too close to wake-up time.
Evening Cardio
Pros:
- Higher body temperature enhances flexibility, strength, and endurance (Chtourou & Souissi, 2012).
- Allows for more meals beforehand, improving glycogen availability for performance.
- Acts as a stress-reliever after a long day.
Cons:
- Increased adrenaline and body temperature can disrupt sleep if performed too late.
- Social or professional commitments may interfere with consistency.
Individual Differences
Chronotypes
Your chronotype—whether you are a “morning person” or “evening person”—influences your energy levels and exercise preferences. A study in the Scandinavian Journal of Medicine & Science in Sports found that early chronotypes performed better in morning workouts, while late chronotypes excelled in the evening (Kunorozva et al., 2014). Adapting your cardio timing to your natural rhythm can enhance adherence and performance.
Sleep Patterns
Sleep quality and duration directly affect exercise performance and recovery. Morning cardio may be unsuitable if it compromises your sleep duration due to an early wake-up time. Similarly, late-night cardio sessions can disrupt sleep by delaying melatonin release. Prioritise a consistent sleep schedule to maximise the benefits of your workouts.
Lifestyle and Preferences
Practical considerations, such as work schedules, family commitments, and gym availability, also dictate the best time for cardio. The most effective workout is the one you can perform consistently over the long term. Tailor your training schedule to align with your lifestyle for optimal results.
Practical Tips for Cardio Timing
- Match Your Goals: If fat loss is your primary goal, consider morning fasted cardio. For performance or endurance, late afternoon sessions may be more effective.
- Listen to Your Body: Pay attention to how your body feels at different times of the day. Choose a time when you feel energised and motivated.
- Avoid Overtraining: Space out cardio and strength training sessions to allow adequate recovery. For example, do cardio in the morning and strength training in the evening.
- Stay Hydrated: Dehydration affects performance regardless of timing. Drink water before, during, and after your workout.
- Optimise Nutrition: Tailor your pre- and post-workout meals to your cardio timing. For morning cardio, a light snack like a banana can provide quick energy. For evening sessions, ensure you’ve eaten a balanced meal a few hours beforehand.
Conclusion
The best time of day to do cardio ultimately depends on your goals, physiology, and lifestyle. Morning cardio is ideal for fat loss and cardiovascular benefits, while afternoon or evening sessions are better for performance and endurance. Regardless of timing, consistency, proper nutrition, and adequate recovery are essential for maximising results.
Table of Key Takeaways
| Key Point | Summary |
|---|---|
| Morning Cardio | Best for fat loss and cardiovascular health; benefits from fasted state. |
| Afternoon/Evening Cardio | Optimal for performance, endurance, and high-intensity workouts. |
| Consistency is Key | Choose a time that aligns with your lifestyle for long-term adherence. |
| Adapt to Chronotype | Morning people may prefer early workouts; evening people excel later. |
| Nutrition Matters | Tailor meals and hydration to your workout timing for best results. |
