The Science Behind Brick Training: Why Running After Cycling Feels Like Walking on Cotton

What Is a Brick Workout

A brick refers to a combined training session where two sports are performed back-to-back, with the most classic example being “cycling followed by running.” The origin of the name is debated, but for triathletes, the brick is the only way to simulate the “disconnected-legs feeling after dismounting” in training.

Why Your Legs Feel “Not Your Own” After Dismounting

The heavy, uncoordinated feeling right after you start running is driven by several physiological mechanisms:

1. Impaired Stretch-Shortening Cycle (SSC): Research shows that intense cycling temporarily weakens the muscular elastic rebound capacity needed for running. However, athletes who consistently do brick training experience a significantly reduced negative effect.
2. Delayed Blood Flow Redistribution: While cycling, blood is concentrated in the pedaling muscles and the skin for heat dissipation. When switching to running, the body needs time to redistribute blood flow.
3. Motor Pattern Interference: Cycling is a closed-chain, fixed-trajectory cyclic movement; running is an open-chain, impact-loaded movement. The nervous system needs to “switch programs” anew.

Using the “Attractor Method” to quantify this, research found that after a 40 km bike ride, athletes on average need to run about 679 meters to exit the transition lag phase, with the first kilometer being particularly prone to uncoordinated running form.

Key Adaptations from Brick Training

• Circulatory Adaptation: The body shifts blood from cycling muscles to running muscles more quickly
• Motor Pattern Conditioning: Smoother cadence transitions, reducing mechanical chaos
• Psychological Desensitization: Getting used to that heavy feeling so you won’t panic on race day

A 2026 study further pointed out that millimeter-level adjustments to bike fit settings (saddle height, cleat position) independently affect running economy after dismounting, apart from power output, with one study measuring a 4.7% improvement in running economy after fit optimization. This reminds athletes: brick training isn’t just about building fitness—it’s also a tool for testing whether your fit can “translate into running.”

Weekly Brick Workout Plan Example

Training Key Points

• Transition Fast: Incorporate actual T2 actions (changing shoes, grabbing the race belt) into your rehearsal—the closer to reality, the better
• Spin Out Before Dismounting: In the final few minutes, increase cadence and lower the gear to prepare your legs for the switch
• Not Every Brick Needs to Be Long: A 10-minute brick run often holds more training value due to “carrying fatigue” than a standalone 10-minute easy run
• Frequency Over Intensity: For beginners, a steady weekly brick is more effective than an occasional ultra-long brick

Coach’s Perspective: The essence of brick training isn’t “training harder,” but “teaching the nervous system to switch seamlessly between two movements.” Treat it as skill training, not just fitness training.

Related Reading

• The Science of Brick Training — Muscle Adaptation Mechanisms and Workout Design for Bike-to-Run Transitions
• Triathlon Brick Training: Designing Leg Adaptation Workouts for Running Immediately After Cycling
• The Physiology of Brick Training: Why Your Legs Feel Like Lead After Dismounting
• Brick Training: Why Your Legs Won’t Obey After Dismounting? Breaking Down the Physiological Impact of Bike-to-Run Transitions and Training Methods