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