About Athletes physiology and dietology

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“Athlete physiology and dietology” can cover a wide syllabus. A useful structure is:

Exercise energy systems and muscle physiology
Cardiovascular, respiratory, endocrine, and thermoregulatory adaptations
Training, recovery, sleep, overtraining, and injury prevention
Sports nutrition: energy availability, carbohydrate, protein, fats, and hydration
Micronutrients and common deficiencies
Nutrition by sport and training phase
Body-composition goals and safe weight-making
Supplements, doping risks, and practical meal planning

At a high level, athletic performance depends on matching the dominant energy system to the activity, maintaining adequate energy availability, and periodizing carbohydrate, protein, fluids, and recovery around training load. The details vary greatly for endurance, strength/power, team-sport, and weight-category athletes.

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“Athlete physiology and dietology” can cover a wide syllabus. A useful structure is:

Exercise energy systems and muscle physiology
Cardiovascular, respiratory, endocrine, and thermoregulatory adaptations
Training, recovery, sleep, overtraining, and injury prevention
Sports nutrition: energy availability, carbohydrate, protein, fats, and hydration
Micronutrients and common deficiencies
Nutrition by sport and training phase
Body-composition goals and safe weight-making
Supplements, doping risks, and practical meal planning

Exercise physiology
Sports nutrition and meal planning
Hydration and electrolytes
Supplements and anti-doping
Diet plans for endurance, strength, or team-sport athletes

Explain the main energy systems used during exercise

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exercise AND bioenergetics

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exercise energy systems ATP phosphocreatine glycolytic oxidative physiology

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https://www.ncbi.nlm.nih.gov/sites/books/NBK482280

Muscle contraction is powered directly by ATP (adenosine triphosphate). Because stored ATP lasts only about 1 to 2 seconds of maximal effort, muscle continually resynthesizes it through three overlapping energy systems. They do not switch on and off one at a time. All contribute, but their relative contribution changes with exercise intensity and duration.

Energy system	Main fuel / process	Rate of ATP supply	Typical dominant duration	Examples
ATP-PCr (phosphagen)	Stored ATP and phosphocreatine	Fastest	0-10 seconds	Jump, shot put, 1-rep max lift, short sprint
Anaerobic glycolytic	Muscle glycogen or blood glucose, producing lactate	Fast	About 10 seconds to 1-2 minutes	200-400 m running, repeated sprints, hard intervals
Aerobic oxidative	Carbohydrate and fat, with a smaller protein contribution	Slower, highest capacity	Minutes to hours	Distance running, cycling, swimming, recovery between bursts

1. ATP-PCr system: immediate energy

Also called the phosphagen system or alactic anaerobic system.

Muscle contains a very small store of ATP, enough for only about 1-2 seconds of maximal contraction.
Phosphocreatine (PCr) rapidly donates a phosphate group to ADP to remake ATP: [ \text{PCr + ADP} \rightarrow \text{ATP + creatine} ]
It produces energy almost instantly and does not require oxygen.
It supports the highest possible power output, but its supply is very limited. ATP plus PCr generally supports maximal work for about 8-10 seconds.

Athletic examples: 60-100 m sprint start, vertical jump, Olympic lift, throwing event, brief maximal tackle or acceleration.

PCr is rebuilt mainly aerobically during recovery, which explains why rest periods are important between maximal sprints or lifts. Guyton and Hall Textbook of Medical Physiology, p. 1060-1061.

2. Anaerobic glycolytic system: rapid short-term energy

Also called the glycogen-lactic acid system.

When intense exercise continues after PCr falls, the body rapidly breaks down muscle glycogen or glucose through glycolysis.
This can make ATP without directly using oxygen.
Pyruvate formed during glycolysis is converted to lactate when ATP demand exceeds the muscle's oxidative capacity.
It supplies ATP rapidly, though not as rapidly as the phosphagen system, and can sustain very hard activity for roughly 30 seconds to 1-2 minutes.

Athletic examples: 200 m and 400 m running, a long hard shift in ice hockey, 30-90 second intervals, repeated high-intensity efforts in team sport.

Important correction: lactate is not simply a waste product or the sole cause of fatigue. It can be transported and oxidized as fuel by other muscle fibers and the heart. Fatigue in severe exercise reflects several factors, including hydrogen ion accumulation, inorganic phosphate, impaired calcium handling, and declining fuel availability.

The system is useful because glycolysis can generate ATP about 2.5 times faster than oxidative metabolism, but its high rate cannot be maintained indefinitely. Guyton and Hall Textbook of Medical Physiology, p. 1061.

3. Aerobic oxidative system: sustained energy

Also called oxidative phosphorylation or the aerobic system.

Occurs largely in the mitochondria.
Uses oxygen to generate ATP from:
- Carbohydrate: muscle glycogen and blood glucose
- Fat: intramuscular triglycerides and circulating fatty acids
- Protein: usually a small contribution, increasing somewhat during prolonged exercise or inadequate carbohydrate availability
ATP production is slower than anaerobic pathways, but the total capacity is much larger.

Athletic examples: jogging, long-distance cycling, marathon running, rowing, prolonged swimming, and recovery periods between high-intensity actions.

At low to moderate intensity, fat contributes substantially. As intensity rises, carbohydrate becomes more important because it can provide ATP at a faster rate. During very prolonged exercise, fat becomes increasingly important, but carbohydrate availability still strongly affects the ability to sustain higher intensities. More than 95% of energy for sustained long-term muscle contraction is from oxidative metabolism. Guyton and Hall Textbook of Medical Physiology, p. 1061.

How the systems work together

Consider a 400 m race:

Start and initial acceleration: ATP-PCr dominates.
Middle phase: anaerobic glycolysis makes a major contribution.
Throughout the race: aerobic metabolism is also active and its contribution rises as the event continues.

Similarly, during a football match or basketball game, the aerobic system supports overall movement and recovery, while ATP-PCr and glycolysis provide the bursts for sprinting, jumping, and rapid changes of direction.

Training adaptations

Sprint and strength training improves PCr availability, glycolytic enzyme activity, and tolerance of repeated high-intensity work.
Endurance training increases mitochondrial density, capillary supply, oxidative enzymes, and the capacity to use fat, preserving glycogen.
Interval training develops both aerobic capacity and the ability to repeat high-intensity efforts.

A recent systematic review on maximal exercise energy contribution highlights that aerobic and anaerobic contributions are best viewed as simultaneous and changing continuously, rather than as isolated systems that take turns (2026 systematic review).

About protein

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athletes AND protein intake

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International Society of Sports Nutrition protein exercise position stand protein intake athletes

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PMID: 39628467

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https://jissn.biomedcentral.com/articles/10.1186/s12970-017-…

Protein for athletes

Protein provides amino acids needed to repair and build muscle, support enzymes and immune function, and help recovery from training. It is not the main fuel for exercise in a well-fed athlete. Carbohydrate and fat normally provide most energy; protein contribution rises when exercise is prolonged, glycogen is low, or overall calorie intake is insufficient.

Muscle is in constant turnover: protein synthesis and breakdown occur every day. Training temporarily increases breakdown and sensitizes muscle to dietary amino acids. The recovery period, together with adequate protein and total calories, is when net muscle protein gain occurs. Bailey and Love's Short Practice of Surgery, p. 27.

Practical daily targets

Athlete / goal	Suggested protein intake
General healthy adult	About 0.8 g/kg/day
Endurance training	1.2-1.6 g/kg/day
Team-sport or mixed training	1.4-1.8 g/kg/day
Strength, power, hypertrophy	1.6-2.2 g/kg/day
Calorie deficit or weight loss while resistance training	Often 1.8-2.4 g/kg/day, individualized

For most regularly training athletes, 1.4-2.0 g/kg/day is a well-supported general range. The higher end is commonly useful for resistance training, high training volumes, low energy availability, or dieting. The ISSN position statement supports this overall range for exercising people.

Example: a 70 kg strength athlete aiming for 1.8 g/kg/day needs about:

[ 70 \times 1.8 = 126\text{ g protein/day} ]

Distribution and timing

Total daily intake matters most. Still, spreading protein across the day improves opportunities to stimulate muscle protein synthesis.

Aim for about 0.25-0.4 g/kg per meal, usually 20-40 g for many adults.
Eat protein in 3-5 meals, spaced roughly every 3-4 hours.
Include a protein-containing meal soon after training if a normal meal will not be eaten within a few hours.
A pre-sleep serving of protein can be useful for athletes who struggle to meet daily protein needs, particularly during heavy resistance training.

Each serving should contain enough essential amino acids, especially leucine, which helps initiate muscle protein synthesis. The ISSN statement suggests about 20-40 g of high-quality protein per serving, often providing roughly 1-3 g leucine.

Best food sources

Animal sources

High-quality, complete proteins with all essential amino acids:

Milk, Greek yogurt, cottage cheese
Eggs
Chicken, fish, lean meat
Whey or casein protein powder

Plant sources

Can fully support athletic goals if total intake and variety are adequate:

Soy foods: tofu, tempeh, soy milk
Lentils, beans, chickpeas
Peas and pea-protein products
Seitan
Nuts, seeds, whole grains

Plant-based athletes may benefit from choosing varied sources and aiming toward the upper end of the protein range, because digestibility and leucine content can be lower in some plant foods. Soy is a particularly useful complete plant protein.

Whey, casein, and supplements

Whey protein: rapidly digested and rich in leucine. Convenient after training.
Casein: slower-digesting dairy protein. Useful as a filling snack or before sleep.
Protein powder: optional. It is food in a convenient form, not a requirement.
BCAAs: generally unnecessary if daily protein is already sufficient, because complete protein supplies BCAAs plus the other essential amino acids required for muscle protein synthesis.

Protein is not a substitute for carbohydrate

For endurance events and hard training, inadequate carbohydrate reduces training quality and glycogen availability. Combining protein with carbohydrate after demanding or prolonged sessions can support recovery, especially when rapid refueling is needed. A 2024 systematic review found modest endurance-related benefits in some settings, particularly when protein was co-ingested with carbohydrate, rather than from high protein intake alone (systematic review, PMID 39628467).

Safety

In healthy people, intakes in athlete-appropriate ranges are generally considered safe. However:

Do not let high protein crowd out carbohydrate, healthy fats, fruits, vegetables, and micronutrient-rich foods.
Drink according to thirst and exercise conditions. Extra protein does not automatically require excessive water intake.
Anyone with chronic kidney disease, a history of kidney stones, pregnancy, or a medical dietary restriction should obtain individualized advice before using high-protein diets or supplements.

Who discovered vitamin

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Casimir Funk coined vitamin term 1912 history reliable source

The term “vitamin” was coined in 1912 by Polish biochemist Casimir Funk. He originally called them “vitamines”, from “vital amines,” because he believed these essential substances were amines.

However, vitamins were not discovered by one person alone. Earlier researchers, including Christiaan Eijkman, showed that substances in unpolished rice could prevent beriberi. Funk helped establish the broader concept that dietary deficiency causes diseases such as beriberi, scurvy, rickets, and pellagra. History of Funk's term

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