Load Management Part 1- The Stress System: Understanding the Stress Response in Strength Training

Introduction

In this series, I’m driving home the point that the purpose of exercise is to cause adaptation to produce meaningful results, and that continual, progressive adaptation only happens through training.  Training is strategically planned and regulated exercise. You need training NOT exercise.

Training is fundamentally a process of applying stress to the body to elicit adaptation. This stress isn't limited to physical exertion; psychological factors such as motivation, anxiety, and cognitive demands also play crucial roles. By comprehensively understanding The Stress System we can optimize training protocols to see long term and short term benefits, achieve timely goals, and achieve our client/athlete’s purpose.

In training we call the total amount of Stress applied to an athlete/client through a training unit (Rep, Set, Day, Week, Block) the Load.  The total Work done is called the External Load.  The level of stress a particular individual experiences from a given external load is known as the Internal Load.  

Prescribing a regulating loads through training to cause long term progressive development and short-term performance peaks for an athlete(s) is the art of personal training and strength & conditioning coaching; developing physical attributes and abilities on our athletes/clients' quest for health, wellness, and performance.

📈 The Biological Law of Adaptation

At the core of all effective training lies the Biological Law of Adaptation — the principle that the body responds specifically to the demands placed upon it. This concept is foundational in strength and conditioning and is often referred to as the SAID Principle (Specific Adaptation to Imposed Demands).

In practice, this means that the body only adapts to what it is repeatedly exposed to. If you train for maximal strength, your neuromuscular system adapts to produce more force. If you train for endurance, your aerobic systems improve oxygen delivery and energy efficiency. If you expose the body to no structured stress at all, it adapts to that too — by becoming weaker, less resilient, and less efficient.

The Stress System: A Dual-Pathway Response

Adaptation arises from the body's ability to respond to various stressors through two primary biological pathways:

1. The Hypothalamus-Pituitary-Adrenal (HPA) Axis

• Activation: The HPA Axis is triggered by prolonged exposure to significant physical and/or psychological stressors.

• Hormonal Response: Secretion of cortisol, a glucocorticoid hormone that aids in energy mobilization and modulates inflammation.

• Implications: While acute elevations in cortisol facilitate adaptation, chronic elevations can lead to maladaptive outcomes such as impaired recovery and immune suppression.

Reference: Hormonal adaptation and the stress of exercise training: the role of glucocorticoids

2. The Sympathetic-Adrenomedullary (SAM) Axis

• Activation: The SAM Axis responds to immediate stressors, initiating the "fight-or-flight" response.

• Neurotransmitter Release: Rapid release of epinephrine (adrenaline) and norepinephrine, enhancing cardiovascular output and energy availability.

• Implications: Acute activation enhances performance; however, chronic over-activation can lead to issues such as hypertension and anxiety.

Reference: Resistance training as an acute stressor in healthy young men

Mediators: Bridging Stress and Adaptation

The body's response to stress involves various mediators that influence adaptation:

• Norepinephrine & Epinephrine: Facilitate immediate energy mobilization and heightened alertness.

• Cortisol: Regulates metabolism and inflammatory responses; essential for adaptation but detrimental if chronically elevated.

• Cytokines: Involved in inflammatory responses; their regulation is crucial for recovery and adaptation.

Reference: The stress-buffering effect of acute exercise: Evidence for HPA axis negative feedback

Receptors: Gatekeepers of the Stress Response

Mediators exert their effects by binding to specific receptors:

• Adrenergic Receptors (α1, β1, β2): Mediate cardiovascular and metabolic responses to catecholamines.

• Glucocorticoid Receptors (GR): Bind cortisol, influencing gene expression related to metabolism and immune function.

• CRH Receptors (CRH-R1, CRH-R2): Modulate the release of ACTH and subsequent cortisol production.

Reference: Molecular aspects of the exercise response and training adaptation

Physiological and Behavioral Adaptations

Effective training engages the HPA and SAM axes driving their mediators to effectively bund to the receptors with induces both physiological and behavioral adaptations:

Physiological Adaptations

• Neuromuscular Enhancements: Better coordination and muscle activation patterns.

• Structural Developments: Increased muscle mass, bone density, and joint integrity.

• Enhanced Energy Systems: Improved efficiency of aerobic and anaerobic pathways.

• Cardiovascular Improvements: Increased cardiac output and oxygen delivery.

Reference: Adaptations to Endurance and Strength Training

Behavioral Adaptations

• Increased Resilience: Improved ability to handle physical and psychological stressors.

• Enhanced Recovery Practices: Adoption of effective rest and nutrition strategies.

• Optimized Stress Management: Development of coping mechanisms to handle training-related stress.

These physiological and behavioral adaptations add up and transform a trainee into a more psycho-physically effective athlete.

Reference: Exercise training and physiological responses to acute stress: study protocol and methodological considerations

Means: The Most Potent Stressors for Driving the Stress Response in Strength Training

Lifting: Strength and Power

To cause a stress response in strength training, the barbell squat, bench press, and deadlift represent the most potent means for developing the strength modalities. These lifts align with our evolutionary history—maximizing force production in shoulder flexion-elbow extension (upper body pressing strength) and hip extension-knee extension (lower body squatting strength) allowed humans to expel threats, project force, and survive violent encounters. The deadlift, meanwhile, represents our maximal pulling strength, essential for survival tasks such as lifting objects or rescuing others. 

Similarly, the snatch and clean & jerk serve as the ultimate power expressions, as power generation was a key determinant of survival in combat and hunting. These exercises hold the highest trainability and adaptation potential because they align directly with our species' evolutionary imperative.

Furthermore, in resistance training, total work (force × distance) represents the quantitative measure of accumulated stress, while intensity (percentage of one-rep max) and training volume (sets × reps) determine the qualitative stress, manifesting in specific physiological abilities.

The connection between the major lifts and our evolutionary survival imperative is why these lifts became the events of the major strength sports: Weightlifting (Snatch, Clean & Jerk) and Powerlifting (Squat, Bench Press, Deadlift).

The major lifts are also the most direct means for developing the spiritual components of the Will, Decisiveness (Weightlifting), and Perseverance (Powerlifting).

Cardio: Running

Like the significant lifts, running naturally aligns with the evolutionary objective of our organism. Along with producing high Force and Power, being able to display high speed (sprinting) and endurance (long distance) through running is crucial for escaping a dangerous situation or chasing (hunting food).  This is why running is the most trainable means of cardio training.

Like lifting, running is also a potent direct spiritual driver. Practicing sprints builds Expedience, while distance running builds Endurance (extending on from the Powerlifting built Perseverance) in the Will. 

For cardiovascular-based activities, the qualitative measure of adaptational stress is determined by the percentage of maximal heart rate (%HRmax) of the effort, while total time spent in that zone determines the overall accumulation of training stress.

Conclusion

Understanding and applying The Stress System in training involves recognizing the intricate balance between stress application and recovery. By managing physical and psychological loads and acknowledging the body's complex response mechanisms, we can design training programs promoting optimal adaptation, performance, and overall health.

Note: The above references provide further reading on the topics discussed and support the concepts presented in this article.

Stay Tuned For The Whole Picture

This article is part of a blog series detailing the ins and outs of fitness training science. If you're a training client or athlete or a potential one, this series will provide you with some info so you will go into your fitness journey armed with the power of knowledge- you'll know what needs to happen. If you are a trainer or coach, this will give you more insight into your process for improving your client's lives and your athlete's performance. The schematic below shows the whole picture of training science; the highlighted part is the idea in this article. Stay tuned to learn all the ins and outs to take your practice to the next level and beyond!