Adaptations to Training: Strength

• Strength = force generated by a muscle or muscle group, through a full range of motion

  • Max strength is also:
  • In 1 max voluntary contraction (MVC)
  • Also called 1 Repetition Maximum (1RM)
  • Is at a particular velocity (= slow)
  • Is related to muscle power & endurance
  • Depends on factors in & outside muscle
  • Relatively specific; little transfer between:
  • Muscle groups
  • Movement types (esp slow to fast)
  • & for activity (as it activates particular muscle groups)
• Muscle Mass Primary Determinant of Strength:

  • Absolute & relative to body mass; both important
  • Relative = % of BM is muscle
  • Muscle proteins continuously synthesised & broken down
  • Net protein synthesis:
  • Balance between the 2 = no growth
  • More synthesis = more muscle proteins
• Muscle Mass is a Primary Determinant of Strength:

  • Several modulators act on muscle to control its protein balance (& hence muscle mass)
  • PA
  • Nutritional status
  • Genetics
  • Nervous system activation
  • Environmental factors
  • Endocrine influences
• How we Generate more Force:

  • Use more or bigger muscle(s)
  • Recruit more motor units
  • Fastest & strongest fibres later
  • Smallest to longest axons (Size principle)
  • They have increase fibres promoter unit
  • Increase firing frequency of motor units
  • Increase co-contraction of antagonists
• Various Aspects & Requirements of Strength:

  • Strength
  • Amount of force
  • F = m * a
  • Power
  • How quickly produce force
  • Work rate
  • (F * d) / t or F * v
  • Strength
  • How long produce force
  • Work capacity
  • F (*d) * t
• Strength Importance:

  • Health & wellness, quality of life (QOL)
  • For elderly - Being able to live independently
  • Sport
  • all types of sport may benefit (if specific)
  • Occupational
  • Physically demanding jobs
  • Overuse injuries (avoiding)
  • Balance between muscle groups: eg back vs core
  • Activities of daily life
  • Prehabilitation & rehabilitation
  • Prior to surgery - go in strong to prepare for after
  • Hobby / preference (to look a certain way)
  • Confidence & self esteem
• Impacts of Resistance Exercise & Health Outcomes:

  • Increase muscle mass
  • Component of lean body mass (that you can change)
  • Lean body mass major determinant of BMR
  • Sythesising, recycling proteins, requires energy
  • Higher BMR w/ more muscle
  • Better down the line if build while younger (as age)
• Impacts of Resistance Exercise & Health Outcomes:

  • Increase protein breakdown (during-) but increase synthesis (after-exercise)
  • Nutritional (esp amino acids), energy state influence
  • Really catabolic - push towards substrate availability (protein breakdown)
  • Synthesis determined by substrate / nutrition available - to build proteins (such as amino acids)
• Impacts of Resistance Exercise & Health Outcomes:

  • Decrease muscle glycogen (via anaerobic glycolysis - is inefficient → chews through glycogen)
  • Dependent on repetitions, load (intensity), length of rest phase (how do resistance training)
  • Enhances uptake of glucose → synthesis of glycogen
• Impacts of Resistance Exercise & Health Outcomes:

  • Dilates muscle arteries, during & after
  • Lowers peripheral resistance (TPR) & BP (afterwards - in response)
  • During goes up, also dependent on muscle mass
  • More constriction in muscle not being used, less local factors for dilation
• Resistance exercise, like aerobic exercise, can help lessen the major modifiable drivers of coronary heart disease (CHD) & diabetes
• Resistance exercise lessen the major modifiable drivers of CHD & diabetes:

  • Better blood glucose regulation (both insulin dependent & independent)
  • Increase muscle mass (more tissue to take up glucose)
  • Contraction (stimulates GLUT4 independent of insulin)
  • Stay open a bit after exercise too, don’t need insulin to take up the glucose into muscle
  • Glycogen depletion increase uptake / glycogen resynthesis after exercise
• Resistance exercise lessen the major modifiable drivers of CHD & diabetes:

  • Reduced insulin secretion (less demand on pancreas)
  • Increase receptor sensitivity
  • Don’t need as much released
  • Increase glucose transporter (GLUT4) molecules in muscle
  • Increase translocation of GLUT4 for given amount of insulin
  • Blood pressure regulation (& reduced after exercise)
• Why we measure Strength:

  • Assess muscular function & functional capacity
  • (predicts longevity)
  • eg grip strength
  • Identify weak muscle groups
  • To strengthen them
  • Inform training & rehab programs
  • Evaluate success of training / intervention (pre- & post-measure differences)
  • Physiological profiling
  • How they are build & what they are good at
• How we measure Strength:

  • Tensiometer:
  • Cheap & versatile, but only isometric strength
  • Resistance machines
  • Free weights
  • Perform actual task(s) required
  • Valid - represents what we are interested in
• How we measure Strength:

  • Isometric (fixed speed) Dynamometer
  • Gives very precise info
  • Safe
  • Reliable
  • Specific velocities & ranges; can have poor validity
  • ie not necessarily transferable to (sporting) activity
• How we measure Strength:

  • 1 Repetition Maximum (1RM)
  • Common
  • Often isometric (dynamic, fixed resistance, ie constant tension)
  • Not always feasible or appropriate to measure actual 1RM
  • Injury, effort, not necessarily specific (to activity of interest), &...
  • Can predict from multiple reps to failure eg
  • 10 RM ~66% 1 RM for untrained
  • 10 ~75-80% 1 RM for trained
• Resistance Training increase Strength via 2 Mechanisms:

  1. Neural & Hypertrophy - neural contribute more at start than hypertrophy
  2. Hypertrophic stimuli occur from first bout; take time for increase protein to become measurable
• Muscular Adaptation:

  • Hypertrophy = the major muscular adaptation to resistance training
  • By overcompensation to unaccustomed volume of force
  • May not necessary ‘damage’ muscle to stimulate hypertrophy
  • Microtrauma: some do & stimulate satellite cells for muscle growth
• Muscular Adaptation

  • Generally, more in those with lower initial strength
  • Strength is proportional to muscle size (cross-sectional area [CSA])
• Muscular Adaptation:

  • Large Male to Female strength differences:
  • 50 % upper body; 30 % lower body
  • No sex effect in relative hypertrophic response to training
  • % gain in muscle mass is very similar - no difference
• Muscular Adaptation:

  • Muscle mass governed by multiple factors:
  • Genetics
  • Fibre type proportions
  • Myostatin (acts to reduce hypertrophic growth, have less → gain larger muscles)
  • Testosterone (anabolic hormone stimulates muscle growth)
  • Hormones acting
  • Systemically (eg Insulin (takes up glucose & amino acids), Testosterone, GH); &
  • Locally (eg IGF-1 - important for hypertrophic response, stimulated by GH)
  • Hence age & sex differences
• Main mechanism of muscle hypertrophy:

  • Stress → Strain → Adaptation
  • Need stress to give strain
  • Mechanical
  • Hormones so increased IGF-1
  • Upregulate protein synthesis
  • Need essential AA
  • As long as have cascade events
• How the muscle gets bigger:

  • By Hypertrophy (bigger cells)
  • Increase SIZE of myofibrils
  • Increase NUMBER of myofibrils
  • Split to form new ones
  • Not Hyperplasia
  • Get more nuclei
  • Additional of Satellite cells
  • esp in growth development & with damage / injury
  • Most important for hypertrophic response = growth of existing fibres
• How muscle gets bigger:

  • By Hypertrophy (bigger cells)
  • Increase SIZE of myofibrils
  • More contractile protein
  • ½ life of contractile proteins is 1-2 weeks
  • Increase NUMBER of MYOFIBRILS
  • They split to form new ones
• How muscle gets bigger:

  • Addition of Satellite cells
  • Primarily in response of injury & growth development
  • Also proliferate in response to growth factor stimulation (eg IGF-1)
  • Inhibited by somatostatin
• Physiology of Hypertrophy:

  • Hypertrophic outcome is variable partly due to complexity of its control
  • Between individuals (genetic, age)
  • Lack of hypertrophy may not reflect on training quality or quantity
  • Also within individuals (esp interference - what else is going on in life)
  • Potentially within muscles
• Physiology of Hypertrophy:

  • Stimuli also include metabolic signal (amplification) eg
  • Arterial occlusion training (= low mechanical loading)
  • Cutting down blood supply
  • Low intensity training to fatigue
  • Using different fibres, fatigue type 1 start using type 2 fibres
• Physiology of Hypertrophy:

  • Optimal protein intake may be ~ 1.6 g/kg/day
  • For young adults only?
  • For well trained only?
  • Energy an dcHO intake can influence
  • Individual energy & CHO needs / demands
  • For given individual can vary on what they are doing & nutritional state
• 
  

  Meta-analyses show effect of Protein intake on Strength & FFM gains with Resistance Training:

  • Muscle specificity?
  • Confounding in methods
  • Ceiling effect?
  • Timing of feeding?
  • How important?
• Meta-analyses show effect of Protein intake on Strength & FFM gains w/ Resistance Training:

  • Effect favoured protein intake
  • Yes, mixed protein supplements show better improvement but no difference w/ normal protein
  • Untrained & elderly show greatest response / responded best (got more to gain)
• Local effects with Resistance Training:

  • Increase connective tissue strength
  • Structural proteins in muscle, plus tendons & ligaments
  • Reduce injury risk
• Local effects with Resistance Training:

  • Hypertrophy causes a “Dilution” effect
  • Decrease capillary density
  • Decrease mitochondrial density
• Local effects with Resistance Training:

  • Increase enzyme concentration
  • Phosphagen system enzymes
  • Possibly glycolytic enzymes (PFK)
  • Dependent how done; typical resistance using phosphagen system; depends how long rest period
• Local effects with Resistance Training:

  • Increase bone mineral content
  • Decrease % of fastest fibres (IIx), but this effect is outweighed by muscle & nerve adaptations, more IIa, fatigue resistant
  • = more gain - but is a trade-off
  • Might be able to tamper to get type IIx back before event
• Recommendations to Increase Strength:

  • Specificity
  • Training for the test (eg 1RM vs dynamometry)
  • Load
  • > 15 sets / muscle / week
  • Volume
  • >15 sets / muscle / week
  • Daily protein intake
  • >1.6 g / kg of body mass / day
  • Inter-set rest
  • 2 - 5 minutes
• Recommendations to Increase Size:

  • Intensity of effort
  • Volitional fatigue & internal focus
  • Volume
  • >10 reps / muscle / week but <15 sets / muscle / week
  • Training frequency
  • >3 sessions / week
  • Daily protein intake
  • >1.6 g / kg of body mass / day
  • Inter-set rest
  • 60 seconds