When it comes to athletics, nutrition isn’t one-size-fits-all. The demands placed on the body during a marathon are fundamentally different from those during a heavy lifting session and therefore, so are the nutritional strategies that support them. This blog compares the distinct dietary needs of cardio endurance athletes to strength athletes.
Understanding the Energy Systems
To understand the nutritional requirements for endurance and strength training, it’s important to first grasp how the body generates energy (aka ATP) during exercise. The body uses three primary energy systems:
- The ATP-phosphocreatine (ATP-PC) system provides immediate energy for high-intensity, short-duration efforts such as sprinting, jumping, or maximal lifting. This system utilizes stored adenosine triphosphate (ATP) and phosphocreatine (PC) within muscle cells to rapidly regenerate ATP anaerobically (without oxygen). Due to the limited intramuscular stores of these compounds, the ATP-PC system can sustain maximal effort for only approximately 8 to 10 seconds before other energy systems must take over.
- As activity continues, anaerobic glycolysis becomes the main energy system, rapidly breaking down carbohydrates without oxygen to fuel efforts lasting approximately 10 seconds to 2 to 3 minutes. This occurs when the demand for oxygen exceeds the body’s ability to deliver it to working muscles. While effective in the short term, this system also generates lactate as a byproduct, which can contribute to fatigue or “the burn.”
- For longer-duration exercise, once oxygen supply meets demand, aerobic (aka oxidative) metabolism, comprising the Krebs cycle and electron transport chain, contributes. This system uses oxygen to metabolize carbohydrates and fats, producing more ATP and with fewer byproducts. It supports activities like marathon running, cycling, or swimming, and is the most efficient system for endurance performance.
Although all three systems operate simultaneously, one will dominate depending on the intensity and duration of activity.
For example, cardio endurance athletes primarily depend on aerobic metabolism, where sprinters may rely more on anaerobic glycolysis. In contrast, strength and power athletes rely on the ATP-PC system and anaerobic glycolysis during training or competition.
| “Fats burn in a carbohydrate flame”
During prolonged exercise, the body relies on both carbohydrates and fats as fuel sources; however, efficient fat oxidation depends on carbohydrate-derived intermediates. Without sufficient carbohydrate stores, fat metabolism slows, potentially reducing endurance performance. Maintaining adequate glycogen levels is therefore necessary for energy production during sustained aerobic activity. |
Macronutrient Requirements
Given that each energy system utilizes distinct fuel sources and is engaged under specific exercise conditions, an athlete’s general macronutrient requirements vary according to their sport and training objectives.
Cardio Endurance Athletes: For endurance athletes engaged in long-duration, steady-state activities such as running, cycling, or swimming, carbohydrate intake is paramount. During exercise, the body breaks down stored carbohydrate (glycogen) through glycogenolysis, releasing glucose directly within muscle cells and into the bloodstream. Concurrently, blood glucose, derived from recent meals or snacks, provides immediate fuel for oxidative metabolism. Together, these sources ensure a continuous supply of glucose to working muscles, sustaining ATP synthesis via aerobic pathways. Maintaining adequate carbohydrate availability helps preserve glycogen stores, delay fatigue, and reduce the risk of muscle catabolism during prolonged activity.
Fat also contributes significantly to energy production, particularly during lower-intensity efforts, as it provides a more energy-dense fuel (9 kcal/g compared to 4 kcal/g for carbohydrates). Its oxidation becomes more prominent once glycogen stores begin to deplete, continuing to support aerobic metabolism. Protein, while important for muscle repair and recovery, is secondary as an energy source; however, without adequate carbohydrate intake, the body may tap into stored protein (i.e., muscle tissue) to convert it into glucose– a process that is not ideal for performance or recovery.
Typically, carbohydrate needs for endurance athletes range from 6 to 12 g/kg/day, with higher requirements corresponding to increased training intensity and duration [1,2]. Protein needs generally range from 1.2 to 1.6 g/kg/day [2].
Strength Athletes: For strength and power athletes focused on activities like weightlifting, or sprinting, protein intake is a top priority. Adequate protein supports muscle protein synthesis (MPS), facilitates post-exercise recovery, and promotes muscle hypertrophy and adaptations2. Protein needs for strength athletes are typically higher than those of endurance athletes, often ranging from 1.7 to 2.0 g/kg/day, depending on training intensity and goals [2].
While protein is critical for building and repairing muscle tissue, carbohydrates also play an important role in supporting resistance training performance. During high-intensity, anaerobic efforts, the body utilizes muscle glycogen as an energy source. Consuming sufficient carbohydrates helps maintain glycogen availability, spares protein from being used as fuel, and enhances training capacity, particularly in multi-set or high-volume sessions. Recommended carbohydrate intake for strength athletes typically ranges from 4 to 6 g/kg/day [3], adjusted for training load and body composition goals.
Dietary fat is not a primary energy source during resistance training; however, it remains essential for hormone regulation, joint health, and other physiological processes [2]. Most strength athletes benefit from moderate fat intake, typically comprising 20 to 30% of total daily energy [2], ensuring it doesn’t displace carbohydrate or protein intake needed for optimal performance and recovery [2].
Need a quick reference? Download this chart.
Timing and Meal Strategies
Strategic meal timing significantly influences both performance and recovery in endurance and strength athletes. See our blogs, What to Eat Before, During, and After a Lifting Session and What to Eat Before, During, and After a Cardio Session for more information about nutrient timing.
References
- Henselmans M, Bjørnsen T, Hedderman R, Vårvik FT. The Effect of Carbohydrate Intake on Strength and Resistance Training Performance: a Systematic Review. Nutrients. 2022;14(4):856.
- American College of Sports Medicine. Nutrition and Athletic Performance. Medicine & Science in Sports & Exercise. 2016;48(3):543-568. doi:https://doi.org/10.1249/mss.0000000000000852
- Abel D, ed. CSCS Nutrition Recommendations | Protein & Carbs for Athletes. www.themovementsystem.com. Published July 5, 2024. Accessed May 30, 2025. https://www.themovementsystem.com/blog/cscs-athlete-nutrition-needs-recommendations
