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Writer's pictureJenaed Brodell

Why Am I So Tired at the Start of Exercise?


Starting a workout with a sense of sluggishness or fatigue can feel frustrating, especially when you’ve geared up to perform at your best. But why does this happen? Let’s delve into the science behind why you might feel tired at the start of exercise and explore actionable strategies to overcome it.

Explination why this occurs
Overcoming exercise fatigue

The Science Behind Early-Exercise Fatigue

1. Transition from Rest to Activity

When your body moves from a state of rest to physical activity, several physiological systems need time to adjust. During rest, your muscles rely primarily on aerobic metabolism, which uses oxygen to produce energy efficiently. However, at the onset of exercise, your muscles suddenly demand more energy, forcing your body to rely temporarily on anaerobic pathways, which produce energy faster but less efficiently. This shift can cause a brief energy lag, leaving you feeling sluggish.


2. Blood Flow and Oxygen Delivery

During exercise, your heart rate increases to pump more oxygen-rich blood to your muscles. This process doesn’t reach its peak efficiency immediately; it takes a few minutes for blood vessels to dilate and for your oxygen delivery system to meet demand. Until then, you might feel out of breath or tired.


3. Glycogen Utilization

Muscles use glycogen (stored carbohydrates) as a primary energy source during exercise. If your glycogen stores are low due to inadequate fueling before exercise, your body struggles to meet energy demands, which can result in early fatigue.


4. Hormonal and Neurological Adaptations

Exercise stimulates the release of stress hormones like adrenaline and cortisol, which help mobilize energy stores and increase alertness. However, these hormonal changes don’t occur instantaneously, contributing to a slow start.


5. Psychological Factors

Mental fatigue, stress, or lack of motivation can also play a role. If your brain perceives the workout as challenging before you’ve even started, it may signal fatigue to conserve energy.


Top Reasons You Feel Tired at the Start of Exercise

  • Inadequate Warm-Up: Your body hasn’t had enough time to transition to activity.

  • Poor Pre-Exercise Nutrition: Low energy availability from skipped meals or insufficient carbohydrates.

  • Dehydration: Even mild dehydration can impair performance and make you feel tired.

  • Sleep Deficit: Inadequate sleep disrupts recovery and energy levels.

  • Overtraining or Under-Recovery: Fatigue may indicate insufficient recovery from previous workouts.

  • Iron Deficiency: Particularly common in athletes, iron deficiency affects oxygen delivery to muscles.


Practical Recommendations to Combat Early-Exercise Fatigue


1. Incorporate a Dynamic Warm-Up

A proper warm-up helps your body transition to exercise by gradually increasing heart rate, blood flow, and oxygen delivery to working muscles. Spend 5–10 minutes doing dynamic movements like arm swings, lunges, or light jogging to wake up your body.


2. Fuel Up Strategically

  • Carbohydrates: Ensure your glycogen stores are topped up. Consume a carb-rich snack, such as a banana or oatmeal, 1–3 hours before exercise. Speak to a sports dietitian for individualised advice as they can tailor an individualised fuelling plan for you.


  • Hydration: Drink water throughout the day and consider an electrolyte drink if your workout is intense or lengthy.


  • Caffeine: A small dose of caffeine 30–60 minutes before exercise can enhance alertness and energy.


3. Check Your Sleep Hygiene

Aim for 7–9 hours of quality sleep each night. Establish a consistent bedtime routine and limit screen time before bed to ensure restful sleep.


4. Monitor Training Load

Avoid overtraining by following a structured plan that incorporates rest and recovery days. Pay attention to how you feel during workouts and adjust intensity accordingly.


5. Address Nutritional Deficiencies

Athletes are prone to deficiencies in iron, vitamin D, and magnesium, all of which can impact energy levels. A simple blood test can identify deficiencies, allowing you to correct them with diet or supplementation.


6. Train Your Mind

Mindset plays a crucial role in early-exercise fatigue. Practice visualization techniques or set small, achievable goals to stay motivated and energized at the start of your workout.


When to Seek Medical Advice

If persistent fatigue occurs even after addressing these factors, it’s worth consulting a healthcare provider. Conditions like anemia, thyroid dysfunction, or chronic fatigue syndrome may require medical intervention.



Feeling tired at the start of exercise is a common experience rooted in the natural physiological and psychological adjustments your body undergoes. By understanding the science and implementing practical strategies like proper nutrition, hydration, and warming up, you can overcome this sluggishness and set yourself up for more effective and enjoyable workouts.

Take control of your energy and performance by making small but impactful changes today. Your best workouts are just around the corner!



References

  1. Brooks, G. A., et al. (2020). Exercise Physiology: Human Bioenergetics and Its Applications.

  2. Ivy, J. L., & Portman, R. (2004). Nutrient Timing: The Future of Sports Nutrition.

  3. Burke, L. M., & Hawley, J. A. (2018). "Carbohydrate availability and training adaptation." Journal of Applied Physiology.

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