skeletal muscle physiology and applications to training
TRANSCRIPT
Skeletal Muscle Physiology
And training for optimal performance through the life time
Jason Cholewa, Ph.D., CSCS
All else being equal…
Tyson Gay Bernard Lagat
Specifically…
• Average human fiber type composition is 50/50– 50% fast twitch– 50% slow twitch
• Elite sprinter: 80/20• Elite weight lifter: 70/30• Elite marathoner: 30/70
Agenda
• Describe the muscle twitch• Discuss muscle fiber types• Discuss and apply fiber type response to
training• Identify changes in aging skeletal muscle• Discuss training for older adults
What is a “twitch”
– Twitch is a single cross-bridge cycle
Sliding filament theory of muscular contraction
How do we classify muscle fibers
• Muscle Fiber Types – Type I (slow-twitch) – Type II (fast-twitch)
Fast Twitch
Slow Twitch
Fiber types display a continuum
• I• IC• IIC• IIAC• IIA• IIAX• IIX
Slow Twitch:Increased period of contraction Requires more time to reach peak forceIncreased period of relaxation Less twitches per unit time
Fast Twitch:Shorter period of contraction Less time required to reach peak forceShorter period of relaxation More twitches per unit time
Fiber and Motor Nerve Diameter
Fasting neural firing yields greater force production
Classifications based upon MHC
Differences in MHC and Force
MHC= myosin heavy chain
Classification based on myosin ATPase
Differences in in myosin ATPase and fuel usage
Rapid contractions require a greater rate of ATP breakdown
Fast Vs. Slow
Motor Unit
All or none principal
• All of the muscle fibers in the motor unit contract and develop force at the same time
• The fibers innervated by a single motor nerve are homogenous
Which fiber does this require most?
True or False
• A single motor unit can consist of BOTH Type I and Type II fibers
What happens to fibers during resistance training?
• A shift of the type of myosin ATPase and MHCs takes place during training.
• Type II and I fibers hypertrophy with resistance training
• Transformations from IIx to IIax to IIa occur
Not in mammals
Why the transition?
Transition is due to stimuli, in this case force and duration
Notice how rapidly IIX burns through ATP compared to IIAX & IIA
Movements requiring longer duration >3 sec (i.e.: heavy squats or high reps) relies heavily on IIA
What type of fiber was most responsible for these match changing spikes?
Improving/preserving “explosive” power
• Training protocols that require maximal force output in a very short duration (< 5-8 sec)
• Examples?– Plyometrics– Dynamic effort training– Reactive training
• May reduce the transition from IIAX to IIA/C
Aging skeletal muscle
• Physical function is decreased with age– Muscle atrophy with aging results from decreases
in both number and size of muscle fibers• Type II fibers are lost• Type I fibers hypertrophy
• Loss of Type II’s = decreased strength and power– Loss of Type II’s associated with loss of bone mass– 10% loss per decade after the age of 40
Aging Muscle
• Loss of power is biggest predictor of frailty and disability
• Reductions in muscle size and strength are amplified in weight-bearing extensor muscles.– Hip extensors are “lost” first– What should (or shouldn’t) we focus their training
on? • (google “weight training elderly”)
Training Application
• Need to increase tension production at high rates of muscular contraction
• Power training (50-60% 1 rm, fast contractions, 3-6 repetitions) may be best for improving or delaying loss of function in the elderly
RESEARCH PROJECTSPerformance for all ages
Inspiration- What can be accomplished??
Ivan Abadjiev is 80 years old!
Frailty and sarcopenia
• Dynapenia is highly associated with frailty• Muscle CSA is reduced by 50% by age 80• Decreases in GH and IGF-1 associated with
sarcopenia
Frailty and Fatness
• high fatness associated with lower muscle quality and an accelerated loss of lean mass– Elevated resistin production• Reduced ability of insulin to suppress muscle protein
breakdown
– Elevated interlukin-6 production• Promotes muscle protein catbolism
– Reduced GH/IGF-1 responsiveness with inactivity
Muscular Power and Frailty
• Muscular power positively associated with ability to perform daily tasks– Power output at 40% MER associated with
improved gait and stair climbing• Power decline is nearly 2-fold that of strength
between ages 65 and 80
Betaine
• Trimethylglycine found in dark greens and extracted from sugar beets
• Organic osmolyte with high absorption qualities
• Average human consumption is 50-100 mg/day
Betaine and Body Composition
• Improves body composition when combined with training in healthy men (Cholewa)– Increased muscle mass and limb CSA– Reduced body fat mass
Betaine and Strength
• Results have been conflicting, but all studies show some positive results– Increased max effort isometric bench press and
squat force production (Lee et al.)– Increased repetitions at > 90% peak/mean force
(Hoffman et al.)– Increased bench press and back squat work
capacity (Cholewa et al., Trepanoski et al.)
Betaine and Power
• No differences in vertical jump or bench press power (Hoffman et al.)
• Trend for improved vertical jump (Cholewa)– Did not train specifically for power
• Increased vertical jump and bench press throw power (Lee et al.)– Had 2 power training sessions over 14 days
Betaine and Anabolic Signaling
• Increased GH and IGF-1 in humans (Apicella)• Increased insulin mediated protein synthesis (Akt)
(Apicella et al.)• HCTL inhibits insulin stimulated protein synthesis,
increases resistin production, and triggers an immune response– Betaine attenuates dietary rise in HCTL in healthy
subjects (Cholewa)– Betaine decreases HCTL in MTHFR- and BHMT-
deficient patients (Li et al.)
Research Project Specific Aims (#1)
• Compare changes in physical function with changes in muscular performance– Subjects (characteristics and groups)– Training program– Functional tests– Muscular performance
Specific Aim 2
• Compare changes in body composition between groups and compare to changes in muscular performance
Specific Aim 3
• To relate changes in GH and IGF-1 to improvements in body composition, muscular performance, and physical function.– measure GH and IGF-1 at baseline and every 2
weeks for 16 weeks
Potential Faculty Collaborations
• Dr. Flynn – Exercise, aging and the immune reponse
• Tom Carrol – Evaluation of power and torque• Students – opportunity to work with older
adults• Fulfilling current HPL research objectives:– Effect of Nutritional Supplements on Performance
and Biological Markers
Research Inspiration 2Cystic Fibrosis and Resistance Training
Cystic Fibrosis• Exercise improves CF survival – Higher VO2 associated with lower risk of dying
• Aerobic exercise may reduce airway inflammation via mechanical deformation (Cholewa & Paolone, 2012)
Exercise - Limiting Factors
• Peripheral muscle atrophy occurs with disease progression
• Peripheral muscle strength major limiting factor in exercise capacity– In adults with CF (Reilly et al., 2011)
• ~ 62% of young adults with CF either have osteopenia or osteoporosis (Paccou et al., 2010)
CF and Inflammation
• CF patients have higher levels of inflammation• Exercise induced inflammation is lower in
response to HIIT vs. MISS in CF (Nguyen et al., 2011)
• Inflammation accelerates bone loss (Haworth et al., 2004)– IL-6, TNF-α
• Cross sectional studies indicate exercise capacity is associated with higher BMD
Lack of Research
• No intervention studies investigating exercise and BMD in CF (Bradley & Moran, 2011)
• Lack of studies examining inflammatory and growth factor response to resistance training
• Lack of studies investigating work capacity, BMD and muscle adaptations to resistance training in CF
• No studies comparing resistance, aerobic, and combination training in CF
Extended Projects
• Effects of varying intensities of resistance training on muscular strength and function
• Effects of strength gains on VO2, work capacity, bone mineral density, and muscle mass
• Effects of varying intensities and modalities of resistance training on inflammatory cytokines and growth factors
Long Term Goals for CF Research
• Network with Cystic Fibrosis Foundation Mt. Pleasant
• Network with Medical School USC
• Network with Boomer Esiason Fund
• Contribute to ACSM guidelines for exercise testing and prescription in CF
Potential Collaborations
• Dr. Flynn – Inflammation response to exercise in chronic disease
• Dr. Smail – Resistance training in youth subjects
• Students – opportunity to work with youth with reduced physical capacity