@kaisin82
Just came across this (new) vid...... Shd be pretty accurate info.
Exactly what i was talking about earlier in my wall-of-text posts to you
(paiseh, but dont think it is fruitful to just quickly gloss over things). Multifactoral, but she is dwelling more on the calves aspect.....that's why i mentioned about the calves endurance test, other than the specific strengthening needed.
If you wanna try next time post race, also can. I tested a few times before, have been slowly inching up..... now is around mid 40s reps. I think 30-35 is the bare minimum pure / long distance runners should shoot for. But note, it's gonna get you pretty sore next few days if you are not into strengthening before so do be careful.
She also talked about only heavy + slow calf work producing meaningful adaptations.
Summary
This video addresses
late race fatigue in runners and triathletes, focusing specifically on the
calf-Achilles tendon complex and its critical role in endurance running performance. Late race fatigue is multifactorial, involving glycogen depletion, central fatigue, dehydration, thermoregulation, and neuromuscular fatigue. However, this presentation highlights a less discussed but highly trainable mechanical factor: the
loss of Achilles tendon stiffness and subsequent calf muscle inefficiency, which significantly increases the metabolic cost of running during prolonged efforts.
Key Concepts and Findings
- Durability: A newly recognized key component of endurance performance, defined as the metabolic cost of running increasing over time even at a constant pace.
- Propulsive Work Distribution:
- Ankle (via Achilles tendon): ~54%
- Knee: ~23%
- Hip: ~23%
- The Achilles tendon acts as an elastic spring, storing and returning energy passively, which reduces metabolic cost.
- The calf muscle fibers contract more slowly due to the tendon’s spring action, optimizing muscle efficiency (enthalpy efficiency) at around 20% of maximum shortening velocity.
- Dynamic creep: After prolonged loading (e.g., 90 minutes of running), the Achilles tendon loses stiffness (~9% reduction), requiring calf muscles to contract faster and more, moving them away from their efficiency sweet spot.
- This leads to a 1.3% worsening of running economy after 90 minutes, with tendon stiffness explaining 43% of this change.
- As calf muscles fatigue (up to 19-20% torque reduction after a hard 10k run), the body redistributes work from the ankle to the knee and hip, which are metabolically less efficient.
- This redistribution is more pronounced in:
- Less trained runners
- Runners with weaker calf-Achilles systems
- At higher intensities
- Gender differences and running styles affect redistribution patterns (e.g., some female recreational runners shift load directly from ankle to hip, bypassing the knee).
Summary Timeline of Fatigue Mechanism
| Stage | Description | Effect on Running Economy / Mechanics |
|---|
| Fresh State | Achilles tendon stiff, calf muscles contract at optimal speed | Efficient propulsion; low metabolic cost |
| After prolonged load | Achilles tendon undergoes dynamic creep, loses ~9% stiffness | Calf muscles shorten faster, less efficient; metabolic cost rises |
| Muscle fatigue onset | Calf muscle strength drops (~19-20% reduction after intense runs) | Load redistributes to knee and hip; less efficient propulsion |
| Late race performance | Increased metabolic cost, potential stride breakdown and fatigue symptoms | Performance declines, especially in long races (marathon, Ironman) |
Quantitative Data from Key Studies
| Variable | Value / Change | Source / Notes |
|---|
| Ankle propulsive work | ~54% | Fletcher & Macintosh, 2018 |
| Knee & Hip propulsive work | ~23% each | Fletcher & Macintosh, 2018 |
| Tendon stiffness reduction | ~9% after 90 minutes running | Fletcher & Macintosh, 2018 |
| Running economy worsening | 1.3% after 90 minutes running | Fletcher & Macintosh, 2018 |
| Calf peak torque reduction | 19-20% after hard 10k run | Multiple studies |
| Redistribution ankle work | Drop from 52% to 44% (recreational runners) | Seno et al., 2018 |
| Redistribution knee work | Rise from 29% to 33% (recreational runners) | Seno et al., 2018 |
| Redistribution hip work | Rise from 19% to 23% (recreational runners) | Seno et al., 2018 |
| Muscle tendon training results | +10% calf strength, +31% tendon stiffness, -4% metabolic cost | Bowman et al., 2021 intervention study |
Training Recommendations
- Primary focus: Improve plantar flexor muscle strength and Achilles tendon stiffness to delay fatigue-related efficiency losses.
- Effective protocol (Bowman et al., 2021):
- Five sets of four isometric ankle plantar flexion contractions
- 90% maximal voluntary contraction
- 3 seconds contraction, 3 seconds relaxation
- 3-4 sessions per week for 14 weeks
- Results from this protocol demonstrated:
- 10% increase in plantar flexor strength
- 31% increase in tendon stiffness
- 4% reduction in running metabolic cost (significant for performance)
- Tendon adaptation requires high strain (4.5-5%); lighter, high-rep calf raises are insufficient for tendon stiffness improvements.
- Alternative or complementary approach:
- Heavy slow resistance training (1-6 RM, 3s concentric + 3s eccentric tempo)
- Targets tendon strain through slow, controlled movements
- Plyometricsimprove stretch-shortening cycle efficiency but should be programmed carefully to avoid overload:
- Low amplitude, high frequency hops and bounds (e.g., single-leg pogos, A-skips)
- Avoid excessive volume and allow 48-72 hours recovery between heavy strength and plyometric sessions
- Whole lower limb strength is essential:
- Heavy squats for glutes and quads (3-4 sets of 4-5 reps)
- Hamstring exercises (e.g., curls, staggered stance Romanian deadlifts)
- Hip abduction/external rotation exercises (e.g., cable hip abduction, side planks)
- This comprehensive approach supports:
- Metabolic efficiency
- Injury prevention
- Load management when redistribution to knee/hip occurs
Key Insights and Conclusions
- Late race fatigue is a complex, multifactorial problem, but the calf-Achilles system plays a central mechanical role.
- Loss of Achilles tendon stiffness significantly increases metabolic cost before muscle fatigue occurs.
- Calf muscle fatigue leads to inefficient load redistribution to less economical hip and knee muscles, compounding fatigue and performance decline.
- Targeted strength training of the calf-Achilles complex can improve tendon stiffness, muscle strength, and running economy by up to 4%.
- A combined training approach including heavy isometrics, heavy slow resistance, plyometrics, and whole lower body strength is optimal.
- Tendon adaptations are slow, requiring consistent training over 12-14 weeks or more; benefits are best realized as a long-term commitment.
- Individual responses vary; programming should be personalized based on athlete needs, pain, recovery capacity, and training context.
- This approach is particularly valuable for:
- Runners experiencing late race mechanical fatigue
- Recreational or older athletes with weaker calf-Achilles systems
- Triathletes entering running with pre-fatigued calves from cycling
Glossary of Terms
| Term | Definition |
|---|
| Dynamic creep | Temporary elongation/stretching of a tendon under repeated loading |
| Enthalpy efficiency | Muscle efficiency based on contraction speed; how effectively metabolic energy is converted to work |
| Isometric contraction | Muscle contraction without changing length |
| Plantar flexion | Movement of pointing toes downward, involving calf muscles |
| Stretch-shortening cycle | Muscle-tendon action during rapid eccentric-concentric movements, enhancing elastic energy use |
This video provides an evidence-based, practical framework to understand and address a key mechanical contributor to fatigue in endurance racing. By improving the
calf-Achilles tendon complex's strength and stiffness, athletes can
delay fatigue-related metabolic cost increases and better maintain performance in long-distance events.
