Physiological Adaptations to Resistance Training

Bioenergetic Responses and Adaptations to Resistance Training

Acute and Chronic Adaptations

  • Resistance training elicits both acute and chronic bioenergetic and physiological adaptations.
  • Neuromuscular adaptations and muscle fiber type alterations occur during training and detraining.
  • Hypertrophic adaptations and cell signaling responses are also observed.

Bioenergetic Responses (Tess et al. Study)

  • An older study by Tess et al. involved biopsies and blood samples to assess bioenergetic changes during resistance training.
  • Exercises included front squat, back squat, leg press, and leg extension with 6-10 reps.
  • The back squat load was around 100 kg.
Key Bioenergetic Variable Changes:
  • ATP and PCR content decreased.
  • Free creatine content increased.
  • Glucose and lactate concentrations increased significantly.
  • Glycogen levels decreased.

Peak Power Output (Gross Diaga et al. Study)

  • A 2010 study by Gross Diaga et al. examined peak power output profiles with 5 and 10 repetitions.
  • Peak power was maintained better with 5 reps compared to 10 reps, which showed tapering.
Effects on Bioenergetic Variables:
  • PCR content drastically reduced with both 5 and 10 reps.
  • Free creatine content increased accordingly.
  • ATP to ADP and ATP to AMP ratios decreased, especially with 10 repetitions.
Glycolytic Intermediates:
  • Glucose-6-phosphate and fructose-6-phosphate increased.
  • Lactate production significantly increased post-exercise with 10 repetitions (1.86 to 7.1 to 17.2).
  • pH levels decreased, indicating a more acidic environment.
ATP Production from Anaerobic Metabolism:
  • Changes in glycogenolysis and ATP turnover were observed.
  • Five vs. 10 repetitions showed different effects.

Peak Power Output and Training to Failure

  • Peak power output was assessed with 5 sets of 10 repetitions to failure versus 10 sets of 5 repetitions not to failure.
  • Peak power reduced heavily in the group performing 5 sets of 10 reps to failure.
  • Training to failure with higher repetitions is not ideal for developing neuromuscular characteristics like explosiveness or power.
Bioenergetic Responses to Different Exercise Protocols:
  • Changes in inosine monophosphates (IMP), PCR content, creatine phosphate, and lactate production.
  • Distinct differences between 10-repetition and 5-repetition groups.
  • ATP to AMP concentration reduced more for the 10-repetition group.

Muscle Glycogen Response to Resistance Training (Greg Halfettle Study)

  • A study published by Greg Halfettle in February examined the acute muscle glycogen response.
  • Muscle glycogen content decreased by about 40.7% post-resistance training.
  • Subjects fed carbohydrates (CHO) showed less glycogen depletion compared to a placebo group.
Effects of Muscle Glycogen:
  • Muscle glycogen can be significantly impacted depending on the training plan and overall workload.
  • Low glycogen levels can alter cell signaling and negatively impact hypertrophy by affecting mTOR pathway activation.
Glycogen Concentration and Resistance Exercise:
  • Exercise with normal muscle glycogen still results in a reduction post-exercise.
  • Starting exercise in a glycogen-depleted state leads to a greater decrease in glycogen content.

Dietary Intervention and Exercise (Crew et al. Study)

  • Eight male cyclists underwent a dietary intervention with low carbohydrate (2% of dietary intake) and high carbohydrate (80% of dietary intake) groups.
  • Diets were isocaloric and lasted three days.
Exercise Intervention:
  • Day 1: Glycogen depletion (60 minutes cycling at 68% VO2 max, 30 minutes two-arm cycling).
  • Day 2: 75 minutes cycling at 68% VO2 max, six sprint intervals (1 minute on, 1 minute off), 30 minutes two-arm cycling.
  • Day 3: 3 sets of 10 repetitions at 70% of 1RM with 2 minutes recovery.
  • A randomized counterbalanced crossover design was used, with one week separating each trial.
  • Biopsies were performed before, 20 seconds after, and 10 minutes after exercise.
Study Results:
  • Differences in ERK 1/2 phosphorylation were observed between low-carbohydrate and high-carbohydrate groups.
  • mTOR phosphorylation tended to be higher in the high-carbohydrate group, especially 10 minutes post-exercise.
  • AKT signaling increased 10 minutes after exercise in the high-carbohydrate group, but no change in the low-carbohydrate group.
Discussion:
  • Low muscle glycogen results in an attenuation of protein synthesis.
  • This may occur due to increased AMPK activation during energetic stress.
  • Proper resistance training in a well-fed state increases AKT signaling, stimulating the mTOR pathway and muscle protein synthesis.
  • In a low-glycogen state, resistance training stimulates the AMPK pathway, inhibiting mTOR signaling and reducing muscle protein synthesis.

AMPK Activity and Glycogen Levels

  • AMPK activity in resting human muscle and its activation during exercise are related to the fuel status of the cell.
  • Low glycogen levels increase AMPK activity, which downregulates mTOR activity, reducing protein synthesis.
  • In general, low glycogen is detrimental to muscle protein synthesis.

Chronic Bioenergetic Changes with Training

  • Endurance training (black circles) and sprint/resistance training (white circles) lead to distinct chronic bioenergetic changes.
  • Sprint and resistance training result in increases in sodium and potassium pump activity and improvements in GLUT4 transport proteins and lactate hydrogen transport.
  • Endurance training improves fatty acid transport and increases glucose transporters.
  • Distinct bioenergetic adaptations occur between endurance and resistance training.