Hypertrophy and Intensity

Volume and Intensity in Hypertrophy

• The volume of training and intensity are interconnected when discussing hypertrophy.
• To increase volume load,
  • Increase volume with lower loads to high levels.
  • Lift heavier things more frequently.
• Lifting heavier things is generally favored for increasing muscularity and strength.

Research by Professor Andy Fry

• Professor Andy Fry's research is highly regarded in the strength and conditioning field.
• His 2004 paper is considered seminal.
• Hypertrophy of individual fibers:
  • Type II fibers show greater hypertrophic responses with higher intensities (Figure 5).
  • Type II fibers are better at expressing higher forces and are more adaptable.
  • Type I fibers will hypertrophy with higher intensity loadings, contrary to popular belief.
  • Low loads with high volumes can still stimulate hypertrophy.
• Relative intensity accounts for $35\%$ of the variance in hypertrophy of type II fibers.
• Load is a significant factor; it explains about $18\%$ of the variance in type I fiber hypertrophy.

Examples from Various Sports

• Weightlifters have a higher type II fiber percentage than bodybuilders.
• Powerlifters also have higher type II fibers.
• Bodybuilders tend to have greater type I fiber hypertrophy.
• Powerlifters:
  • Use higher loads, typically in the 5-1 rep range.
  • Train in the strength zone.
• Weightlifters:
  • Train in the strength and power zone.
  • Achieve higher volumes through multiple sets.

Regression Lines and Fiber Types

• Regression lines can show relationships between type I, type II, type 2a, and type 2x fibers.
• Relative intensity accounts for approximately $12\%$ of the explained variance in type 2A fibers.
• Relative intensity accounts for approximately $20\%$ of the explained variance in type 2X fibers.
• Adaptation occurs with low loads (e.g., $40\%$
• Higher loads stimulate greater amounts of hypertrophy.

Impact of Intensity on Fiber Types

• Study by Measure et al. examines fiber cross-sectional area in controls, bodybuilders, and powerlifters.
• Bodybuilders generally have greater fiber cross-sectional area because they train for hypertrophy.
• Power athletes aim to hypertrophy type 2X and 2A fibers.
• Bodybuilders exhibit significant hypertrophy of hybrid fibers, affecting overall muscle fiber size.
• Bodybuilders have greater amounts of type I fiber.

Type II to Type I Fiber Area Ratio

• A high type II to type I fiber ratio is desirable for enhancing sports performance.
• Weightlifters have a higher ratio than powerlifters.
• Both weightlifters and powerlifters have better ratios than bodybuilders.
• A 2:1 fiber type ratio in bodybuilders is suboptimal for performance.
• Training methods for bodybuilders are not ideally suited for training athletes.

Optimal Hypertrophic Stimulus

• Professor Fry suggests training between $75-95\%$ of 1RM to maximize hypertrophic stimulus.
• Adequate volumes are necessary in this intensity zone.
• Heavier than $95\%$ of 1RM does not allow for adequate volume to maximize hypertrophy.
• Hypertrophy is possible with low loads but is not optimal.
• Optimal hypertrophy occurs between $75\%$ and $95\%$ of 1RM.

Logic Behind the Intensity Range

• The most muscular individuals in the weight room typically train in higher intensity ranges with adequate volumes.
• Training volume between 6 and 12 repetitions is recommended (ACSM position stance).

Age Considerations

• Younger and older individuals respond differently to training.
• Younger individuals have a better anabolic environment.
• Younger individuals respond well to loadings between $60\%$ and $90\%$ of 1RM, showing significant fractional synthesis rate stimulation.
• Older adults also benefit from $60\%$ to $90\%$ of 1RM for fractional synthesis rate changes.
• Higher loads are superior to low loads (less than $45\%$, for stimulating muscle growth.
• Younger individuals get a greater stimulus from $60\%$ to $90\%$ than older individuals due to factors like the leucine threshold and hormonal environment.
• Both groups experience hypertrophic stimulus from training with loads between $60\%$ and $90\%$ of 1RM.

Low Load Hypertrophy: Is It Worth It?

• Hypertrophy can be stimulated with sets at $30\%$ of 1RM to failure.
• Higher loads are generally preferred for fewer reps.

Hypothetical Mechanisms for Low Load Hypertrophy

Indirect Mechanisms (Fatigue-Induced)

• Training to failure with low loads.
• Increased mechanical tension.
• Increase fiber recruitment (potential changes in calcium dynamics and fiber type-specific hypertrophy).
• Altered metabolic stress.

Muscle Damage Model

• Unlikely mechanism.
• Alterations to proteins that might change myostatin responses.
• Hormone response (definitely an unlikely mechanism).

Direct Mechanism

• Most likely related to inflammation.
• Reactive nitrogen species and oxidative stress.
• Alterations in metabolites (lactate plays a small role).
• Potentially related to mechanical tension, metabolic stress, inflammation, reactive nitrogen species, and oxidative stress.

Load, Muscle Recruitment, Damage, and Fatigue

• Low loads require significant fatigue to recruit a large number of fibers when training to failure (Fluiling's model).
• High loads recruit fibers quickly, cause some muscle damage, and induce fatigue by the end of the set.

mTOR and AKT Signaling

• Multiple sets performed with $30\%$ to failure or $80\%$ to failure both stimulate an mTOR response (promotes protein synthesis).
• AKT shows a similar response.
• P70 S6K (downstream) gets a greater stimulus from higher loads regardless of sets.
• There has been a very minimal correlation between P70 S6K, threonine three eighty nine, the change in that cell signaling compound and quadriceps volumes.

Volume and Strength Gains

• 30% to failure for three sets and 80% to failure for three sets resulted in similar quadriceps volume changes after ten weeks.
• Strength gains were greater with heavier loads, even with only one set.
• The goal of resistance training should be to improve functionality, not just increase muscle mass.
• Muscle mass growth without improved force generating capacity is less useful.

Motor Unit Activation

• Phillips and Byrd suggested that training to failure activates high-threshold motor units, stimulating protein synthesis.
• Miller's study at Trent Herte's lab (University of Kansas) showed that higher intensities activate different motor units.
• Higher loads activate higher threshold motor units.
• Maximizing hypertrophy requires lifting heavy things to activate type II fibers.
• Low load and high load both increase hypertrophy, but higher loads enhance performance more as it makes us much stronger.

Strength Gains Comparison

• Strength gains are almost double with higher loads after 30 sessions of lower body training.
• Light leg training (15% of 1RM to failure) vs. heavy leg training (70% of 1RM).

Meta-Analytic Data

• Brad Schoenfeld's meta-analytic study shows that higher loads stimulate greater hypertrophy.
• Updated study in 2017 confirms that 1RM is maximized with higher loads.

Hypertrophy and Fiber Types

• When loads are equated, there isn't a big difference in hypertrophy between high load and low load.
• Higher loads tend to stimulate greater type I fiber hypertrophy.
• Type II fibers show greater hypertrophy with higher loads.

Ramifications of Low Loads Lifted to Failure

• McKay's study from Joel Kramer's lab indicates increased injury risk with very low loads for high volumes trained to failure.

Case Study: Exertional Rhabdomyolysis

• A college-aged female experienced exertional rhabdomyolysis after completing 30% of 1RM for three sets of 30-40 repetitions in the bicep curl.
• Total reps: 143, total volume load: 2,574 kilograms.
• Significant muscle soreness and swelling developed.
• Creatine kinase levels were extremely high (11,000 to 12,000 units per liter), indicating significant muscle damage.

Conclusion on Low Load Training

• Low load volumes with RM loads don't magnify hypertrophic gains and don't maximize strength; plus, there is a risk of rhabdomyolysis.
• Low load training isn't smart training despite scientific evidence of its effectiveness.

Quotes from Experts

• Professor Fry: "What is so great about more muscle mass if force producing capacities, capabilities excuse me, not accompany it, unless you are a bodybuilder."
• Professor Fry: "All the mechanisms proposed for low load hypertrophy are such weak candidates for explaining hypertrophy."
• Professor Fry: "The interpretation of the data rather than its accuracy is often the issue when looking at hypertrophy."
• Professor Fry: "Heavier loads are more effective at stimulating hypertrophy, and the data on using light loads is usually from studies that use untrained individuals."
• Professor Stone: "The mechanisms for low load hypertrophy are different than those for high load training."
• Professor Stone: "Most of the studies involve subjects who are not very well trained initially."

Summary of Findings

• Higher load training results in greater strength gains.
• Higher load training can produce similar or greater hypertrophy than low load training, depending on the session structure.
• Low load training can increase hypertrophy but requires impractical volumes and training to failure.
• If you want to get bigger, lift heavy things more frequently.