WK2

Unit Housekeeping

  • Labs in Week 3 & 4 will not be in JO19.149
  • Check Canvas for updates later in the week
  • Progression Quiz #1 due next week
  • Lifting starts tomorrow; dress appropriately

Lecture Objectives

  • Review the physiology of force expression
  • Review morphological adaptations to resistance training
  • Review the endocrine adaptations to resistance training
  • Review the performance adaptations to resistance training

Neural Adaptations to Resistance Training

  • Multiple factors combine to allow for modulation of force expression
    • Motor unit recruitment
    • Rate coding
    • Both can be impacted or improved by exposure to heavy resistance training

Motor Unit Recruitment

  • Governed by the "Size Principle"
  • Increased force output occurs through the addition of motor units
  • Smaller fibers are recruited first, followed by medium and large fibers as tension increases.

Rate Coding

  • Refers to the frequency that motor units are activated at
  • Increased activation frequency leads to increased force.

Impacts of Resistance Training on the Neuromuscular System

  • Resistance training improves force production in multiple ways:
    • Increased motor unit recruitment
    • Improved motor unit synchronization
    • Increased motor unit firing rate
  • Also improves the rate of force development
  • Adaptations are most efficiently generated by high-intensity contractions
    • Vecchio et al. (2019) J Physiol 597: 1873-1887
    • Stone MH, Cormie P, Lamont H et al. Developing strength and power, in: Strength and Conditioning for Sports Performance. I Jeffreys, J Moody, eds. Oxon, UK: Routledge, 2016, pp 230-260.

Morphological Adaptations to Resistance Training

  • Chronic exposure to resistance exercise leads to increases in muscle cross-sectional area (CSA)
  • After exposure to heavy resistance training, all fibre types increase in CSA
  • The magnitude in increase in CSA is proportional to the training stimulus applied

Muscular Hypertrophy

*Body composition and muscle thickness of participants, before and after 6 weeks of resistance training

10-SET (n=10)5-SET (n = 9)
PrePost
Body mass (kg)
Total77.5 ± 7.179.2 ± 6.9
Lean61.8 ± 7.463.0 ± 6.9
Fat12.1 ± 6.212.7 ± 5.7
%Fat16.2 ± 7.816.7 ± 7.0
Regional lean body mass (kg)
Trunk28.5 ± 4.228.8 ± 4.0
Arms8.6 ± 0.98.9 ± 0.8
Legs20.6 ± 2.621.1 ± 2.4
Muscle thickness (mm)
Triceps42.0 ± 6.646.5 ± 4.1
Biceps34.6 ± 4.134.9 ± 2.2
Anterior thigh53.3 ± 7.854.4 ± 7.2
Posterior thigh66.7 ± 6.568.9 ± 6.7

*Amirthalingam et al. (2017) J Strength Cond Res 31: 3109-3119

Muscular Hypertrophy

  • Davies et al. (2016) Sports Med 46: 487-502

*Volume controlled
* Drinkwater et al. [14]
* Folland et al. [35]
* Izquierdo et al. [31]
* Rooney et al. [32]
* Mean Effect
*Volume uncontrolled
* Izquierdo-Gabarren et al. [37]
* Kramer et al. [38]
* Sampson and Groeller [36]
* Sanborn et al. [44]
* Mean Effect
*Mean effect, total

Muscular Hypertrophy

Refalo et al. (2025) PeerJ 13: e19042

StudyEffect SizeConfidence IntervalFavors
Walsh (2009)0.30[0.14, 0.5]
Sterczala (2024)0.28[0.11, 0.5]
Hubal (2005)0.26[0.1, 0.45]
Kosek (2006)0.23[0.05, 0.43]
Abou Sawan (2021)0.22[0.03, 0.45]
Ivey (2000)0.22[0.02, 0.45]
Abe (2000)0.22[0.07, 0.37]
Moesgaard (2022)0.22[0.04, 0.42]
Nunes (2020)0.21[0.01, 0.44]
Abou Sawan (2022)0.21[-0.02, 0.44]
McMahon (2018)0.20[-0.03, 0.43]
Ribeiro (2014)0.19[0.01, 0.38]
Alway (1992)0.19[-0.03, 0.39]
Rissanen (2022)0.19[-0.04, 0.39]
Peterson (2010)0.18[-0.01, 0.36]
Coratella (2018)0.18[-0.06, 0.38]
O'Hagan (1995)0.18[-0.06, 0.39]
Cureton (1988)0.18[-0.04, 0.37]
Hurlbut (2002)0.17[-0.06, 0.37]
Grandperrin (2024)0.17[-0.05, 0.37]
Schwanbeck (2020)0.17[-0.02, 0.34]
Fernandez-Gonzalo (2014)0.17[-0.05, 0.35]
Hammarström (2020)0.17[-0.03, 0.34]
Lundberg (2019)0.17[-0.02, 0.32]
Psilander (2019)0.16[-0.06, 0.34]
Hakkinen (1998)0.16[-0.09, 0.35]
Reece (2023)0.16[-0.03, 0.31]
Kojic (2021)0.14[-0.08, 0.29]
Hakkinen (2001)0.11[-0.17, 0.28]
Pooled Effect0.19[0.11, 0.28]

Muscular Hypertrophy

Refalo et al. (2025) PeerJ 13: e19042

StudyPercentage ChangeConfidence IntervalFavors
Walsh (2009)0.9%[-1.9%, 3.9%]
Sterczala (2024)1%[-2%, 4.7%]
Schwanbeck (2020)0.6%[-2.4%, 3.6%]
Rissanen (2022)0.6%[-2.9%, 3.8%]
Ribeiro (2014)0.7%[-2.5%, 3.8%]
Reece (2023)0.6%[-2.8%, 3.9%]
Psilander (2019)0.6%[-3%, 3.8%]
Peterson (2010)0.7%[-2.6%, 4.2%]
O'Hagan (1995)0.7%[-2.9%, 4.2%]
Nunes (2020)0.8%[-2.6%, 4.2%]
Moesgaard (2022)0.8%[-2.7%, 4.3%]
McMahon (2018)0.7%[-2.9%, 4.1%]
Lundberg (2019)0.7%[-2.7%, 4%]
Kosek (2006)0.8%[-2.2%, 4.2%]
Kojic (2021)0.5%[-3%, 3.6%]
Ivey (2000)0.7%[-2.6%, 4.3%]
Hurlbut (2002)0.7%[-2.8%, 4.1%]
Hubal (2005)0.8%[-2.2%, 4%]
Hammarström (2020)0.7%[-2.5%, 3.9%]
Hakkinen (2001)0.6%[-3%, 4%]
Hakkinen (1998)0.6%[-2.9%, 3.9%]
Grandperrin (2024)0.7%[-2.7%, 4%]
Fernandez-Gonzalo (2014)0.7%[-2.8%, 4.1%]
Cureton (1988)0.7%[-2.8%, 4.1%]
Coratella (2018)0.6%[-2.8%, 3.8%]
Alway (1992)0.7%[-2.7%, 4.2%]
Abou Sawan (2022)0.8%[-2.5%, 4.2%]
Abou Sawan (2021)0.7%[-2.6%, 4.3%]
Abe (2000)0.7%[-1.8%, 3.3%]
Pooled Effect0.7%[-1.5%, 2.9%]

Muscular Hypertrophy

Relative Intensity Effects

Repetition Maximum Effects

VariableType I CSA (μ\mum²)Type II CSA (μ\mum²)ACSA (cm²)MT (cm²)
pre ± SD3277 ± 6924079 ± 119539.10 ± 6.252.12 ± 0.33
post ± SD3720 ± 7935839 ± 139942.53 ± 5.763.62 ± 0.32
g (90% CI)0.56 (0.22-0.89)0.81 (0.37-1.26)0.53 (0.33-0.73)1.47 (0.99-1.95)
Between-Group Effects
pre ± SD3470 ± 7894883 ± 113740.77 ± 9.222.48 ± 0.38
post ± SD3713 ± 9745493 ± 124142.09 ± 8.752.83 ± 0.43
g (90% CI)0.26 (-0.02-0.54)0.49 (-0.05-1.02)0.14 (0.00-0.28)0.80 (0.46-1.14)
Between-Group Effects
g (90% CI)0.48 (-0.35-1.31)0.50 (-0.33-1.33)1.03 (0.20-1.86)0.72 (-0.11-1.55)

Carroll et al. (2019) Sports 7:169

Fibre Type Adaptations

  • No evidence of Type I fibres turning to Type II fibres
  • Hybrid fibres will change structure in response to heavy resistance training
  • Mostly occurs in the early stages of training
  • Adaptive process is reversible. Type IIx -> Type IIxa -> Type IIa

Structural and Architectural Changes

  • Exposure to heavy resistance training induces changes in pennation angle and fascicle length
  • These changes in muscle architecture allow greater force to be applied to the bone and therefore greater outward force expression during movement

Other Morphological Changes

  • Resistance training has substantial impacts on bone and connective tissue structures

Other Morphological Changes

  • Connective tissue also adapts to chronic exposure to high-intensity resistance training
  • Strength and load-bearing capacity adaptations occur at specific locations:
    • Junction between connective tissue and bone
    • Within the body of the connective tissue
    • Within the network of skeletal muscle fascia
  • Stiffness of connective tissue also increases due to high-intensity resistance training exposure

Practical Implications

  • Target high training intensities when seeking changes in morphology
  • Adaptations are proportional to the training stimulus…to a point
  • Training to volitional failure isn’t required to optimize adaptive response

Practical Implications

  • The interplay of morphological and neural adaptations sets the foundation for well-structured training programs
Mesocycle FocusPhysiological Outcome
Strength-EnduranceImprove work capacity
Basic StrengthIncrease muscle CSA
Strength-PowerIncrease force-generating capacity
Strength-PowerImprove rapid force-generating capacity

Endocrine Responses to Resistance Training

*Hormonal Responses
*Hormonal responses to resistance training takes multiple forms
*Acute or transient changes during and after training
*Chronic changes in acute response to training
*Chronic changes in resting concentrations

Acute Responses to Training

  • Exposure to high-intensity resistance training typically leads to:
    • Increases in Testosterone
    • Increases in IGF-1 & GH
    • Increases in Cortisol
  • Changes occur quickly and rapidly stabilize

Chronic Changes to Acute Responses

  • Chronic changes in acute hormonal response to training mirror improvements in muscular force
  • Theoretically allows the individual to better tolerate and sustain higher intensity exercise
  • Limited to no evidence that these changes impact hypertrophic response of skeletal muscle to resistance exercise

Chronic Changes in Resting Hormones

  • Limited evidence that chronic exposure to high-intensity resistance training leads to changes in resting hormone concentration
  • Moreover, there’s evidence that chronic elevation of resting hormones is in fact counterproductive

Cortisol Responses

  • High volumes of training upregulate cortisol release
  • Responsible for portioning of metabolic resources prior to the tissue remodeling stage
  • Provides for an increased ‘pool’ of amino acids

Practical Implications

  • Largest acute changes in hormones occur during high-intensity resistance training coupled with shorter rest periods
  • Schoenfeld et al. (2016) J Strength Cond Res 30: 1805-1812

Practical Implications

  • Hormonal response to resistance exercise may play a role in the adaptive response
  • However, it’s important not to forget the overall goal of your training program
Training GoalRest Period
Strength2-5 min
Power:
Single-effort event2-5 min
Multi-effort event30s to 1.5 min
Hypertrophy≤30s
Muscular endurance30s to 1.5 min

Performance Adaptations to Resistance Exercise

*Impacts of Resistance Training on Performance Outcomes
*Improvements in motor capacities are linked to improvements in performance outcomes
*Athletes
*Sprinting
*Jumping
*Change of direction
*Sports skills
*General population
*Activities of daily living - older adults
*Core motor skills - children

*Suchomel et al (2016) Sports Med 41: 1419-1449
Behringer et al. (2011) Pediatr Exerc Sci 23: 186-206

Impact of Resistance Training on Sprinting Performance

  • Adaptations to resistance training display a negative relationship with changes in sprint performance
  • Kadlec et al. (2023) Sports Med 53: 313-325

Impact of Resistance Training on Sprinting Performance

  • Improvements in relative strength are closely linked to improvements in performance
    • Pre: 1.78 ± 0.27 x BW
    • Post: 2.05 ± 0.21 x BW
    • Comfort et al. (2012) J Strength Cond Res 26: 772-776

Impacts of Resistance Training on Change of Direction Performance

  • Improvements in motor capacity improve COD performance
  • However…
  • Appleby et al. (2020) J Strength Cond Res 34: 54-64

Impacts of Resistance Training on Change of Direction Performance

Adaptive responses can be task-specific
*Appleby et al. (2020) J Strength Cond Res 34: 54-64

Impacts of Resistance Training on Sports Skills

PretrainingPosttrainingDifferenceES
Squat (kg)126 ± 18135 ± 18
Bench (kg)113 ± 14115 ± 15
Relative squat (kg·kg −1)1.37 ± 0.131.46 ± 0.1510.69Moderate
Relative bench (kg.kg-1)1.23 ± 0.151.26 ± 0.140.14Trivial
CMJ peak power (W)4,639 ± 7404,843 ± 7710.27Small
PPU peak power (W)1.486 ± 3801.663 ± 3900.46Small
Tackling ability (%)70.0 ± 0.174.0 ± 0.10.26Small
Velocity into contact (m·s)3.03 ±0.383.06 0.320.08Trivial
  • Speranza et al. (2016) J Strength Cond Res 30: 336-343

Impacts of Resistance Training on Sports Skills

  • Speranza et al. (2016) J Strength Cond Res 30: 336-343
  • R2=0.29R^2 = 0.29

Impacts of Resistance Training on Motor Skills

ZpESSENGroups
Throwing vs. Running0.690.49
Throwing vs. Jumping0.690.49
Jumping vs. Running0.040.97
Throwing0.990.4111
Jumping0.540.1050
Running0.530.1523
  • Behringer et al. (2011) Pediatr Exerc Sci 23: 186-206

Impacts of Resistance Training on Motor Skills

ExerciseSetsRepetitionsRest interval
Part A: Plyometric training
1/2 squat3560
Lateral bound with stick3560
Single leg push off (low box)3560
90° spin jump3560
Part B: Resistance training
Back squat3860
Front squat3860
Medicine ball static lunge3860
Military press3860
Horizontal pull-up3860
  • Hopper et al. (2017) J Strength Cond Res 31: 1165-1176
ExerciseSetsRepetitionsRest interval
Part A: Plyometric training
1/2 medicine ball squat jump3560
Medicine ball lateral bound3560
Single leg push off (low box)3560
180° spin jump3560
Part B: Resistance training
Back squat3860
Incline Bench Press3860
Split squat-BFE3860
Chin-up3860
Forward Alternating Lunge3860
Romanian Deadlift3860
  • NMST: Experimental Group |\n* Score: 6-6+, 2-, 0; |\n*

Impacts of Resistance Training on Activities of Daily Living

Change (Nm)Change (# of modifications)Change (sec)
Change in knee extension workChange in task modificationChange after
Change in knee flexion workfunctional trainingControlperiod
Resistance trainingResistance + functional trainingTraining
Resistance + functional training
Functional training

Practical Applications

  • Improvements in motor capacities from resistance training have positive impacts across a range of tasks
  • Important to remember the purpose of your position when designing resistance training programs

Questions?

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  • Email: s.guppy@ecu.edu.au