Swimming and Carbohydrates: Glycogen Storage Strategies for Long-Distance Training

Introduction

The importance of carbohydrates for swimmers cannot be overstated. Swimming is a high-intensity aerobic sport, and its primary energy source is glycogen stored in muscles and the liver. Once glycogen is depleted, athletes experience the so-called “hitting the wall”—swim speed drops sharply, technique falls apart, and willpower is exhausted. For competitive athletes who train twice a day, how to fully replenish glycogen within a limited time is a core issue that directly affects training quality.

Glycogen Basics

Glycogen is a polymer of glucose, stored in two main locations:

• Muscle glycogen: approximately 300–500 g (varies by muscle mass), primarily used by the working muscle groups
• Liver glycogen: approximately 90–110 g, used to maintain blood sugar and supply the brain and other tissues

The intensity of swim training (typically 65–85% of VO₂max) makes muscles rely primarily on carbohydrates for fuel. A 90-minute moderate-to-high intensity session can deplete 60–80% of muscle glycogen. If there is insufficient replenishment between morning and afternoon sessions, the starting glycogen level for the afternoon workout may already be below optimal.

Training Volume Determines Carbohydrate Needs

For example, a 65 kg athlete training 2 hours per day needs approximately 325–455 g of carbohydrates daily, equivalent to the carbohydrate content of about 6–8 bowls of white rice.

Glycogen Recovery Strategies on Double-Session Days

Double-session days (e.g., training 90 minutes at 6 AM and again at 4 PM) pose the greatest challenge for glycogen management:

Immediate post-morning-session replenishment (30–60 minutes after training):

• Fast carbohydrates + protein (ratio of approximately 3:1–4:1)
• Example: 2 sweet potatoes (about 50 g carbs) + unsweetened soy milk
• Or: sports recovery drink + 2 bananas

Lunch (between the two sessions):

• A carbohydrate-focused meal, consuming 70–100 g of carbs
• Example: a pork chop rice meal (with extra rice) + soup

2 hours before the afternoon session:

• Ensure lunch has been digested; a light snack can be added
• Example: toast + low-fat yogurt, or sweet potato + tea egg

Mid-Session Supplementation for Long-Distance Training (Over 90 Minutes)

For athletes preparing for marathon swimming or triathlon, training sessions may exceed 90–120 minutes. Mid-session supplementation is needed:

• Replenish 30–60 g of fast carbohydrates every 45–60 minutes
• Forms of mid-session supplementation during pool training: diluted sports drinks, energy gels
• Open-water training: prepare banana slices and diluted sports drinks on the support boat

Practical Recommendations

• Ensure every daily meal includes sufficient staple foods; do not treat carbohydrates as a food that “needs to be restricted”
• During high-volume periods (pre-competition overload weeks), proactively increase intake of white rice, sweet potatoes, and whole wheat bread
• On rest days, moderately reduce carbohydrate intake (by 20–30%); on training days, maintain high carbohydrate intake
• Three days before competition, adopt a carbohydrate-loading strategy (see the pre-competition nutrition article) to maximize glycogen stores
• If fasting morning swims are unavoidable, consume at least 20–30 g of fast carbohydrates (such as a banana) before training to prevent dizziness from liver glycogen depletion
• Whole grains and refined carbohydrates each have pros and cons: choose refined carbohydrates before training (quick digestion); choose whole grains after training or on a daily basis (stable blood sugar)

Conclusion

Carbohydrates are the “fuel” for swimmers, and glycogen management is the core of maintaining training quality. Understanding the carbohydrate needs corresponding to your daily training volume, replenishing properly between double sessions, and designing a mid-session fueling plan for long-distance training will allow you to complete every workout at your best. Do not let the “low-carb diet” trend affect your training performance. Swimmers need carbohydrates—this is science, not an excuse.

Related Reading

• Dietary Strategies for Swimmers: Carbohydrate Timing
• Carbohydrate Loading Before Swim Meets: The Three-Day Pre-Competition Meal Plan
• Pre-Competition Nutrition for Swimmers: Carbohydrate Loading Strategy for the Three Days Before a Race
• Fueling Strategies for Long-Distance Swim Races: Energy Preparation for 1500m and Beyond