Continuous Glucose Monitoring (CGM) in Cycling Training: Life After Supersapiens

At the end of 2023, Supersapiens, the most well-known CGM brand in the cycling world, announced it was suspending operations, leaving many athletes who relied on real-time glucose data caught off guard. But the application of CGM in sports did not end with this. In fact, with technological advances and more brands entering the market, this field is evolving rapidly.

The Relationship Between Blood Glucose and Athletic Performance

Basic Physiology

Blood glucose (the concentration of glucose in the blood) is one of the primary fuel sources for the brain and muscles. Normal fasting blood glucose is approximately 70-100 mg/dL, and it fluctuates during exercise due to increased muscle uptake and glycogen breakdown.

Blood glucose changes during exercise:

1. Low intensity (Zone 1-2): Blood glucose typically remains stable or declines slowly, as fat oxidation provides most of the energy
2. Moderate intensity (Zone 3-4): Blood glucose is gradually depleted; if not replenished after 2-3 hours, it may drop below 60 mg/dL
3. High intensity (Zone 5+): Blood glucose may spike briefly (stress hormones promote glycogen breakdown), followed by a rapid decline

The Impact of Hypoglycemia

When blood glucose drops below 60 mg/dL, you may experience:

• Decreased focus and impaired judgment
• Reduced coordination (increased danger on descents)
• Mood instability (irritability, anxiety)
• Significant drop in muscle power output
• In severe cases: dizziness, blurred vision, numbness in extremities

This is what cyclists commonly call “hitting the wall” (bonk).

The Problem with Hyperglycemia

Conversely, consuming too many high-GI foods before exercise can cause blood glucose to spike to 180+ mg/dL, and the subsequent insulin response may result in:

• Rebound hypoglycemia
• Unstable power output in the early stages of exercise
• Reduced fat oxidation efficiency
• Gastrointestinal discomfort

The Practical Value of CGM in Training

1. Optimizing Pre-Race Meal Strategies

CGM allows you to find the pre-race diet that works best for you:

Traditional advice vs. CGM personalized discoveries:

Traditional advice says “eat low-GI carbs 3 hours before the race,” but CGM data often reveals enormous individual variation:

• One person’s blood glucose spikes to 200 mg/dL 30 minutes after eating a bowl of white rice, while a fellow rider only reaches 140 mg/dL
• The same person eating the same food may have completely different glucose responses on high-stress days
• For some, the optimal pre-race meal is actually coffee + peanut butter whole wheat toast (a low-GI combination)

Practical application:
Test different breakfast combinations on training days, recording:

• Meal timing and content
• Blood glucose curve response
• Subjective feelings and power data during the ride
• After 3-4 tests, find “your optimal pre-race meal”

2. Fueling Timing During Rides

One of the greatest values of CGM is helping you build the intuition for “preventive fueling”:

Traditional approach without CGM:

• Relying on feel: “I think I’m getting hungry” → fuel
• Problem: by the time you feel hungry, blood glucose may have already dropped below 70 mg/dL

CGM-guided approach:

• Observe the downward trend in blood glucose and start fueling when it reaches 90-100 mg/dL
• Learn the glucose response time of different fuel products (gels ~10-15 minutes, energy bars ~20-30 minutes)
• Build a personalized fueling schedule

3. Monitoring Training Adaptations

Long-term CGM use can reveal metabolic improvements from training:

• Fat Adaptation: After prolonged aerobic training, blood glucose declines more slowly at the same intensity (better at utilizing fat)
• Improved Carbohydrate Tolerance: Well-trained athletes have a more moderate glucose response to carbohydrates
• Recovery Quality: The speed at which blood glucose returns to baseline after training reflects recovery status

Options After Supersapiens

Currently Available CGM Systems

Abbott FreeStyle Libre 3

Originally for medical use, but applicable to sports:

• 14-day continuous monitoring
• Glucose data updated every minute
• Waterproof design (can ride in the rain)
• Pairs with smartphone via NFC or Bluetooth

How to obtain in Taiwan:

• Requires a physician’s prescription (typically from an endocrinologist or metabolism specialist)
• Price approximately NT$2,000-2,500 / per sensor (14 days)
• Some clinics offer “athlete metabolic assessment” services and can issue prescriptions

Dexcom G7

Features:

• 10-day monitoring period
• Real-time continuous data transmission (not intermittent)
• Customizable high/low glucose alerts
• Slightly higher accuracy than Libre

How to obtain in Taiwan:

• Also requires a physician’s prescription
• Higher price, approximately NT$3,000-4,000 / per sensor
• Currently lower availability in Taiwan

Lingo by Abbott (Consumer Version)

Launched in select markets in 2024:

• Over-the-counter consumer CGM, no prescription needed
• Comes with a dedicated app providing dietary and exercise recommendations
• Not yet officially available in Taiwan, but can be obtained through proxy purchasing

Alternative Approaches: Glucose Optimization Without CGM

If obtaining a CGM is difficult, the following methods can also improve your glucose management:

1. Traditional Blood Glucose Meter Spot Checks

• Purchase a standard glucose meter available at pharmacies (approximately NT$1,000-2,000)
• Measure at key time points: upon waking, 30/60/90 minutes after meals, before and after training
• While not continuous, this builds a basic understanding of your glucose responses

2. Standardized Fueling Plan
A general fueling guideline based on sports science research:

Ride Duration	Carbohydrate Recommendation
< 60 minutes	No fueling needed (water only)
60-150 minutes	30-60g carbs/hour
150-180 minutes	60-90g carbs/hour
> 180 minutes	80-120g carbs/hour (requires gut training)

3. Subjective Sensation Scale
Train yourself to recognize the body’s signals of glucose changes:

• Starting to feel “empty” → possibly 80-90 mg/dL → time to fuel
• Focus drifting → possibly 70-80 mg/dL → fuel immediately
• Legs feeling weak, cold sweats → possibly < 60 mg/dL → emergency fueling

Practical Glucose Management Strategies for Taiwanese Cyclists

Long-Distance Rides (e.g., Around-the-Island, Wuling)

The night before:

• Dinner focused on moderate-GI carbs (brown rice, sweet potatoes)
• Avoid excessive fiber (more sensitive stomach the next day)
• Finish eating before 21:00

Race-day breakfast (2-3 hours before departure):

• White rice + fried egg + banana
• Or: toast + peanut butter + fruit juice
• Avoid: overly sweet milk tea, creamer-based drinks

During the ride:

• Fuel every 20-30 minutes (don’t wait until you’re hungry)
• First half: energy bars + water
• Second half: energy gels + sports drinks (need faster carbohydrate absorption)
• Convenience store stop choices: bananas, onigiri, sports drinks

Within 30 minutes after training:

• Recovery meal with a carbohydrate-to-protein ratio of 3:1
• Convenient options in Taiwan: chocolate milk + onigiri from the convenience store

Adjusting for Taiwan’s Weather

In hot, humid conditions:

• Blood glucose fluctuations may be exacerbated (stress hormones rise)
• Increased sweating leads to dehydration, affecting glucose readings
• It is recommended to increase fueling frequency (small amounts every 15–20 minutes)
• Electrolyte replenishment is just as important as carbohydrate intake

CGM technology allows us, for the first time, to “see” the body’s real-time metabolic state during exercise. Even after Supersapiens’ departure, this field will only continue to thrive. For cyclists in Taiwan, there’s no need to rush after the latest technology, but understanding the principles of glucose management and building good fueling habits will have a profound impact on your riding performance and safety.

Related Reading

• Blood Glucose and Athletic Performance: The Science of Stable Blood Sugar, and the Truth and Hype Behind CGM Continuous Glucose Monitoring
• A Complete Guide to Blood Sugar-Stabilizing Diets for Athletes: GI/GL, Meal Timing, and Race-Day Fueling
• Hypoglycemia Management for Cyclists: Identifying, Preventing, and Treating Low Blood Sugar in Training and Racing
• Nutritional Management of Diabetes and Exercise: A Coach’s Field Notes on Blood Sugar, Carbohydrate Adjustments, and Hypoglycemia Prevention