Optimal loading involves prescribing an exercise stimulus that promotes positive tissue adaptation, restoring function in patients undergoing rehabilitation and improving performance in healthy athletes. Implicit in optimal loading is the need to monitor the response to load, but what constitutes a normal response to loading? And does it differ among tissues (e.g., muscle, tendon, bone, cartilage) and systems?
This article explores the “normal” tissue response to loading schema and demonstrates the complex interaction among training intensity, volume, and frequency, as well as the impact of these training variables on the recovery of specific tissues and systems.
1. Tissue Response to Load is Variable
Early research demonstrated that the biochemical response of a tissue depended on the type of training performed. Orchard et al. (2015) demonstrated that acute and chronic loads had differential effects on tendon, bone, joint, and muscles. High chronic loads might be protective against some injuries (e.g., muscle injuries) but predictive of other injuries (e.g., joint injuries), while tendon injuries occur most frequently in response to large spikes and troughs in acute load.
- Tendon: High-intensity and maximal-effort running has been shown to alter tendon structure for 2 days [3, 4], with tendon structure returning to normal within 3–4 days.
- Bone: Bone cells desensitise quickly to repetitive loading, with almost all mechanosensitivity lost after as few as 20 loading cycles, but is 90% restored within 8 h of rest.
- Muscle: Eccentric exercise-induced muscle damage can take 72 hours or longer to fully recover.
These findings highlight the diverse tissue responses to an exercise stimulus. Practitioners might be optimally loading one tissue, but sub-optimally loading another.
2. Part 1: From Tissue to System—Different Loads Create Different Responses
2.1 Physiological Responses to Exercise and Training
- Acute and Chronic Adaptations to Training Stress:
- Endurance Training: Increases in mitochondrial biogenesis, capillary density, and cardiac output lead to improved oxygen delivery and exercise capacity. High-intensity interval training (HIIT) and sprint interval training (SIT) can also improve endurance capacity.
- Strength and Power Training: Early gains in strength are primarily due to neural adaptations. Later, increases in muscle cross-sectional area contribute significantly to strength gains.
- Muscle Adaptations: Eccentric exercise is crucial for developing muscle architecture, but it also leads to significant muscle damage and delayed-onset muscle soreness.
- Tendon Adaptations: Tendons adapt to mechanical loading by increasing collagen synthesis and stiffness. High-intensity contractions and longer intervention periods are more effective in eliciting tendon adaptations.
- Bone Adaptations: Bone adapts to mechanical loading through microdamage and subsequent repair. Repetitive loading can lead to bone fatigue, emphasizing the importance of adequate recovery periods.
2.2 Recovery Timeframes
- Muscle: Recovery from high-intensity training can take 48-72 hours or longer, with factors like intensity and volume influencing recovery time.
- Tendon: Tendons generally require 48 hours of recovery after high-intensity, stretch-shorten cycle activities.
- Bone: Adequate recovery (4-8 hours) is crucial between bone-centric exercises to allow for mechanosensitivity to be restored and maximise bone adaptation.
3. Part 2: Programming Considerations for Practitioners
- Prioritising Tissue and System Loading:
- Maintaining Global Load Capacity:
- During periods of reduced loading (e.g., injury rehabilitation), maintain overall physical activity to prevent detraining effects.
- Systemic loading (e.g., aerobic exercise) helps maintain muscle mass, bone density, and overall health.
3.3 If Unloading is Necessary, Maintain Global Load Capacity
- Benefits of Systemic Loading:
- Maintains muscle mass and strength
- Preserves cardiovascular fitness
- Supports tissue healing through improved blood flow and nutrient delivery
- Minimises the risk of detraining and reinjury
3.4 Consider Recovery Timeframes of Different Tissues and Systems When Determining the “Normal” Response to Load
- Individualised Approach: Recovery times vary significantly between individuals. Factors like age, training experience, genetics, and overall health status influence recovery.
- Monitoring and Adjustment: Continuously monitor training load, recovery, and performance to make necessary adjustments to the training plan.
3.5 Interpreting Training Within an Athlete Monitoring Framework
- Integrate Multiple Data Sources: Combine external load data (e.g., GPS, accelerometers) with internal load measures (e.g., heart rate variability, RPE) and subjective feedback (e.g., soreness, fatigue) to gain a comprehensive understanding of the athlete’s response to training.
4. Advancement of Load–Response Research and Practice
- Continued Research: Further research is needed to refine our understanding of tissue-specific recovery timeframes, particularly in response to different types and intensities of exercise.
- Technological Advancements: Continued development of wearable technology and data analysis tools will improve our ability to monitor training load and athlete response.
- Individualised Approaches:
- Develop personalised training plans that consider individual factors such as age, training experience, and genetics.
- Utilise predictive modelling to anticipate potential injury risks and optimise training strategies.
5. Final Considerations
- Influence of Health and Training Status: Factors like age, chronic medical conditions, energy availability, and training status significantly influence tissue response to loading.
- Importance of Individualisation:
- Recognise that every athlete is unique and requires an individualized approach to training and recovery.
- Consider psychological factors such as stress, motivation, and adherence to the training plan.
Conclusion
Optimising training load requires a nuanced understanding of how different tissues respond to exercise stress. By carefully considering factors such as training intensity, volume, frequency, and recovery time, and by utilising a comprehensive athlete monitoring framework, practitioners can create training programs that maximise performance while minimising the risk of injury.
Disclaimer:
This information is for general knowledge and informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional1 for any health concerns or before making any significant changes to your training program.