Dietary supplements and stimulants

Dietary supplements

Dietary supplements are widely used by athletes to support performance and recovery, but their use carries important considerations for safety and compliance.

Issues with dietary supplements

• Some unscrupulous manufacturers have included banned substances in their products without disclosure.
• The lack of regulation in some markets has led to misleading claims about efficacy.
• Athletes should use third-party tested products (e.g., NSF Certified for Sport, Informed Sport) to reduce contamination risk.

Essential amino acids (EAAs)

EAAs cannot be produced by the body and must be obtained through diet or supplements.

Efficacy of EAAs in performance

• EAAs are necessary for muscle protein synthesis.
• Studies show significant increases in muscle protein accretion when EAA supplementation is combined with resistance training.
• Leucine is the key amino acid responsible for activating muscle growth pathways.

Branched-chain amino acids (BCAAs) and leucine

Among the eight essential amino acids (EAAs), the branched-chain amino acids (BCAAs)—isoleucine, leucine, and valine—play a key role in muscle protein synthesis.

Leucine and muscle protein synthesis

• Leucine is the most critical BCAA for stimulating muscle protein synthesis.
• Leucine activates the mTOR (mechanistic target of rapamycin) pathway, a key regulator of protein synthesis in skeletal muscle.
• Research shows that a leucine threshold of about 2–3 grams per dose is required to maximally stimulate protein synthesis. This amount is typically achieved through high-quality protein sources such as whey, without the need for separate BCAA supplementation.
• Studies indicate that a leucine-enriched essential amino acid (EAA) beverage leads to significantly higher muscle protein synthesis compared to a normal EAA beverage.

Adverse effects of BCAAs

• No known reports or scientific studies have found negative effects from BCAA or EAA supplementation.

Arginine

Arginine is a conditionally essential amino acid involved in protein and creatine synthesis and is a precursor to nitric oxide production.

Claims and scientific findings

• Arginine supplementation is often marketed for its ability to:

  • Increase nitric oxide levels
  • Improve blood flow
  • Enhance exercise performance

• However, scientific evidence does not support these claims in healthy individuals.

• Studies have found that oral arginine supplementation does not increase nitric oxide production beyond levels naturally elevated during exercise.

• No improvements in endurance performance have been reported from arginine supplementation.

Adverse effects of arginine

• Generally well tolerated at normal doses.
• Higher doses (13–30 g) may cause gastrointestinal issues, including nausea, abdominal cramps, and diarrhea.

Beta-hydroxy-beta-methylbutyrate (HMB)

HMB is a metabolite of leucine that has been studied for its role in muscle recovery and protein breakdown prevention.

Efficacy of HMB

• Research has shown that HMB supplementation reduces muscle protein breakdown and has anti-catabolic effects.
• Studies suggest that HMB supplementation enhances strength gains when combined with high-intensity resistance training.
• Untrained individuals benefit more from HMB supplementation compared to trained athletes.

Adverse effects of HMB

• HMB is generally well tolerated, with no significant adverse effects reported.
• Research suggests that HMB supplementation is most effective when combined with an adequate training stimulus.

Beta-alanine

Beta-alanine is a nonessential amino acid that serves as a precursor to carnosine, a key buffer of hydrogen ions (H⁺) in skeletal muscle.

Efficacy of beta-alanine

• Beta-alanine supplementation increases skeletal muscle carnosine levels.
• Higher carnosine levels help buffer acidity in muscle, delaying fatigue during high-intensity exercise.
• Studies have shown that beta-alanine supplementation improves anaerobic performance, particularly in activities lasting 30 seconds to 10 minutes.

Adverse effects of beta-alanine

• The most common side effect is paresthesia (tingling or numbness), especially at higher doses.
• Paresthesia is harmless and typically subsides within an hour after ingestion.

Sodium bicarbonate

Sodium bicarbonate is an alkalizing agent that helps buffer acidity in muscles, delaying fatigue during high-intensity exercise.

Efficacy of sodium bicarbonate

• Studies have shown performance improvements in short-duration, high-intensity activities lasting 60 seconds to 6 minutes.
• Supplementing with 0.3 g/kg body weight of sodium bicarbonate 60 to 90 minutes before exercise has been found to enhance performance.

Adverse effects of sodium bicarbonate

• High doses may cause gastrointestinal distress, including:
  • Diarrhea
  • Nausea
  • Vomiting
  • Cramping
• Dividing doses into smaller amounts throughout the day may help reduce side effects.

Dividing doses into smaller amounts throughout the day may help reduce side effects. A typical effective dose is 0.3 g/kg taken 60–90 minutes before exercise. Split or serial dosing can further reduce GI distress, but sodium bicarbonate should be avoided by individuals who require sodium restriction.

Sodium citrate

Sodium citrate is an alternative buffering agent that reduces intramuscular acidity without the gastrointestinal distress sometimes caused by sodium bicarbonate.

Efficacy of sodium citrate

• Research suggests mixed results, with some studies showing performance improvements, particularly in anaerobic exercise.
• Effective doses range from 0.4–0.5 g/kg body weight, taken 60 to 90 minutes before exercise.

Adverse effects of sodium citrate

• Some individuals may experience gastrointestinal discomfort, but it is generally better tolerated than sodium bicarbonate.

L-Carnitine

L-carnitine is synthesized from lysine and methionine and plays a key role in fatty acid transport into mitochondria for energy production.

Efficacy of L-carnitine

• L-carnitine supplementation is marketed for enhancing fat oxidation and improving exercise performance.
• Studies show limited effectiveness in demonstrating increased muscle carnitine levels.
• Some research indicates potential benefits for recovery and reduced muscle damage.

Adverse effects

• Up to 3 g daily appears well tolerated in short-term studies.
• No significant hematological or metabolic side effects have been reported.
• Long-term effects require further investigation.

Creatine

Creatine is a naturally occurring nitrogenous compound found in muscle, liver, kidneys, and dietary sources (meat, fish).

Importance of creatine in exercise

• Stored as creatine phosphate (CP), it is essential for rapid ATP regeneration during high-intensity, short-duration exercise.
• CP depletion is a major cause of muscular fatigue.

Creatine supplementation and performance

• Increases intramuscular creatine levels by 20-40%.
• Enhances strength and power output in trained and untrained individuals.
• Supports muscle mass gains by increasing cell hydration and protein synthesis.

Creatine loading and maintenance

• Loading phase: 20-25 g/day for 5-7 days.
• Maintenance phase: 2-5 g/day.
• Without a loading phase, full muscle saturation may take 30 days.

Body mass changes from creatine use

• Prolonged use is associated with increased body weight due to greater intracellular water retention and muscle growth.
• Typically results in 1-2 kg (2-5 lbs) increase in body mass.

Adverse effects of creatine

• No significant adverse effects reported in research.
• No evidence supports claims linking creatine to dehydration, muscle cramping, or kidney dysfunction.

Stimulants are widely used in sports for their ergogenic effects, including increased alertness, reduced fatigue, and enhanced confidence.

Stimulants

Caffeine

Caffeine is a widely used stimulant found in coffee, tea, soft drinks, and energy drinks.

Efficacy of caffeine for performance

• Enhances endurance by reducing perceived exertion and delaying fatigue.
• Improves cognitive function and mental alertness.
• Peak effectiveness occurs 60 minutes after ingestion.

Dosage and ergogenic effects

• 3-9 mg/kg body weight, taken 60 minutes before exercise, can enhance endurance.
• No additional benefits seen at doses beyond 9 mg/kg.

Adverse effects of caffeine

• Anxiety, insomnia, tremors, heart arrhythmias at high doses.
• Caffeine is addictive, and withdrawal symptoms include headaches and fatigue.
• High doses (>9 mg/kg) pose potential health risks.

Ephedrine

Ephedrine is a β-adrenergic agonist used for temporary relief of symptoms such as bronchial asthma, nasal congestion, and allergies. It is also popular in bodybuilding due to its thermogenic properties, which can increase metabolic rate and fat loss.

Efficacy of ephedrine

• Studies suggest ephedrine is most effective when combined with caffeine.
• It has been shown to improve endurance performance but has mixed results in anaerobic performance.
• Combination of 5 mg/kg caffeine and 1 mg/kg ephedrine led to ergogenic benefits, but higher doses caused negative side effects.

Adverse effects of ephedrine

• Nausea, vomiting, palpitations, high blood pressure.
• Increased risk of heart complications at higher doses.
• Due to numerous safety concerns, ephedrine has been banned by the FDA and is on the International Olympic Committee’s prohibited list.

Citrus aurantium (“Bitter Orange”)

Citrus aurantium contains synephrine, a β-adrenergic agonist similar to ephedrine, and is marketed as a weight-loss supplement.

Efficacy of citrus aurantium

• Limited research supports its effectiveness in fat loss.
• Some studies suggest small improvements in endurance performance when combined with caffeine.

Adverse effects of citrus aurantium

• May increase blood pressure, especially when combined with other stimulants.
• Lack of long-term safety data prevents it from being widely recommended.

Preworkout energy drinks

Preworkout energy drinks typically contain caffeine, amino acids, vitamins, and herbal extracts and are marketed for enhancing focus, endurance, and strength.

Efficacy of preworkout energy drinks

• Effective for increasing resistance training volume and endurance.
• Not effective for anaerobic performance (e.g., sprinting, agility drills).
• Combination of caffeine and other ingredients may enhance effects.

Adverse effects of preworkout energy drinks

• Excessive caffeine intake can lead to jitters, anxiety, and gastrointestinal discomfort.
• Potential for dehydration if consumed without adequate water intake.