Interval Ratios in the Winter Base Period: How to Preserve Speed in a Low-Intensity-Focused Cycle

Introduction

The winter base period (typically October through January of the following year) is the most important—and most misunderstood—training phase in endurance sports periodization. Traditional thinking holds that the base period should be “only low-intensity riding, with no intervals at all,” but modern training science offers a more nuanced interpretation. A purely low-intensity base period can certainly build the aerobic foundation, but if high-intensity stimulus is completely abandoned for 8–12 weeks, a rider’s neuromuscular capacity, fast-twitch muscle function, and sense of speed will all significantly regress, requiring extra time to “reawaken” these abilities when entering the build period.

Core Goals of the Base Period

Before discussing interval ratios, it’s essential to clarify the core physiological adaptations the base period aims to achieve:

• Enhanced aerobic enzyme systems: Increase mitochondrial density, improving fat oxidation efficiency
• Increased capillary bed density: Improve oxygen delivery to muscle tissue
• Expanded left ventricular volume: Increase stroke volume, raising the ceiling for VO₂max
• Tendon and ligament adaptation: Low-intensity, high-volume training gradually strengthens connective tissue, preventing injuries during high-intensity race season

These adaptations primarily occur during long-duration aerobic riding at low intensity (Z1–Z2), and high-intensity intervals cannot effectively elicit them. This is the scientific basis for “low-intensity-dominant base periods.”

Why Intervals Cannot Be Completely Removed

However, the following physiological capacities will regress in the complete absence of high-intensity stimulus:

Research indicates that even maintaining a small amount (once per week) of neuromuscular high-intensity stimulus during the base period is sufficient to effectively prevent the regression of these capacities, without significantly interfering with low-intensity aerobic adaptations.

Recommended Interval Ratio for the Base Period

The intensity distribution during the base period should follow the “90:10 rule”—that is, 90% of training time at low intensity (Z1–Z2), with only 10% devoted to high-intensity or neuromuscular stimulus.

Using a weekly training volume of 10 hours as an example:

The uniqueness of sprint training: The physiological profile of a 10-second max sprint relies primarily on the ATP-PCr system, does not engage glycolysis, and produces minimal lactate, so it causes very little interference with “aerobic recovery.” This makes it the ideal tool for “preserving a sense of speed” during the base period—its negative impact on aerobic capacity is nearly zero, while its maintenance effect on the neuromuscular system is significant.

Taiwan’s Winter Training Reality

Taiwan’s winter (October through February) presents the following specific circumstances to consider:

• Northeast monsoon and rainfall: Northern Taiwan is rainy in winter, offering fewer opportunities for outdoor long rides; southern Taiwan has clear winter weather, providing a relatively favorable training environment
• Increased indoor training needs: Northern riders can make good use of smart trainers for low-intensity long sessions (riding Zwift free ride or at a fixed pace)
• Holiday disruptions: Training routines are easily disrupted around the Lunar New Year, so flexible volume reductions should be arranged before and after the holidays

Sample winter base period weekly plan (Taipei area):

• Monday: Rest
• Tuesday: Indoor trainer Z2 aerobic ride, 90 minutes
• Wednesday: Rest or an easy short outdoor ride (if weather permits)
• Thursday: Indoor trainer Z1–Z2, 60 minutes, including 6×10-second max sprints (full recovery between reps)
• Friday: Rest
• Saturday: If weather permits, outdoor long ride 3–4 hours (Z2, Yangmingshan or Hsinchu); if raining, indoor trainer 2.5 hours at Z2
• Sunday: Easy recovery ride, 60–90 minutes

Practical Recommendations

1. Schedule sprint training on the day when you feel most energetic in the weekly plan (typically the first training day after a rest day following a long ride), rather than the day before a long ride
2. The “sense of accomplishment” in the base period comes from the steady accumulation of training volume, not the intensity of any single session. Weekly training hours matter more than whether an individual session is hard enough
3. If outdoor riding time is shortened due to weather, do not “make up” the reduced volume with high-intensity sessions—this contradicts the core logic of the base period
4. Perform a Ramp Test or 5-minute all-out test once a month to confirm whether FTP is gradually improving from the high volume of low-intensity training (this is evidence that base period training is working)

Conclusion

The winter base period does not require completely “giving up” interval training. Instead, it’s about adjusting the proportion of high-intensity training to the minimum effective dose needed to maintain neuromuscular capacity—one weekly session of 10-second sprints is enough to preserve the sense of speed built over a season. Spend 90% of your time building the aerobic foundation and 10% preventing speed regression—this is the golden ratio for winter base period training design.

Related Reading

• Off-Season Training for Cyclists: How to Maintain Base Fitness in Winter
• Winter Base Period Training Plan: Building the Fitness Foundation for Next Season
• The Aerobic Base Period: Why You Need Lots of Slow Riding
• Building Aerobic Base Mileage on the Bike: The Importance of Winter Long-Distance Riding