1 Exercise and Aging Skeletal Muscle Reading - Rogers p Brooks - end of Ch 19 Nygard - Musculoskeletal Capacity Outline Body composition changes Changes in muscle function Morphological changes Metabolic capacity Adaptations to training

2 Aging Decline of physiological capacity is inevitable consequence of aging –physical inactivity may contribute to this decline - not predominant explanation Body composition with aging inc % body fat / dec lean body mass –studies illustrate selective decline in sk ms protein vs non muscle protein –body K+ and Nitrogen levels muscle peaks at yrs –decline in X sec area, ms density –inc intra-muscular fat Resting Metabolic Rate (RMR) –decline associated with dec ms mass

3 Muscle Function Decline in ms strength –sig loss of max force production Fig Cross-sec study ages men –inc strength to 30, constant to 50, then decline (24-36%) –similar dec in isometric, dynamic and speed of movement women yrs –dec 35% in strength, 33% in Xsec area –dec 15% / decade after 50 yrs –dec 30% / decade after 70 yrs evidence of selective declines in type II fiber area, no change in type I

4 Size and Strength Decline in strength with aging either loss of muscle mass, or alteration in ms capacity to generate force - motor unit activation / contractile properties MVC / CSA (max vol vs X sec area) –older subject ~70% of young –other studies - women no change –men with age ~ 20 % weaker values for old men similar to women difference in young men may be activity related Fig cadaver study

5 Endurance Capacity Fitts - no difference in fatigability –28 vs 9 month old rats Human studies –maintenance of MV isometric and dynamic strength for 1min similar –at same % of MVC (70 vs young) other studies –greater force loss in 30 sec stimulation –greater relative force loss and reduced capacity to resist fatigue observed slow return to resting function following fatigue test –dec rate of twitch force relaxation and inc half relaxation time

6 Morphology Muscle fiber types –divisions based on physiological, ultrastructural and metabolic characteristics Distribution with aging –may be result of inter-conversion or secondary to preferential loss of specific fiber type Lexell - cadaver studies –~50 % type I in all age groups –found 25% fewer fibers (30-70) –accounting for 18% decline in strength between 20 and % loss of fibers - all types

7 Denervation and Fiber loss What is cause of fiber loss with age –damage to ms cells without regeneration –interruption of m neuron connection Fig 19-9 Brooks - 47% decline EMG studies –# of active motor units dec with age –low threshold M units that remain become larger –elderly - lower # of functioning spinal cord motor neurons Aging and fiber size –no sig change in type I fiber size –sig dec in type II fiber size ~26% –(age 20-80) accounts for dec strength

8 Capillarization and Metabolic Capacity Observe 25 % dec in cap density % dec in cap / fiber ratio –* screened for activity level - truly sedentary - still may be confounded –inconclusive evidence Metabolic Capacity and Aging Study enzymatic activity –marker enzyme glycolysis, Krebs, ETC, Beta oxidation, ATP synthesis Glycolytic Capacity considerable evidence glycolytic enzyme activity and high energy phosphates not adversely affected

9 Respiratory Capacity Scandinavian studies - no change in mito ox capacity B - HAD, CS later studies –~25% dec in men and women –40% less O2 uptake capacity contrast - Scandinavian may not be truly sedentary - activity inc mito Adaptation to Endurance Training healthy sedentary - ~10% decline per decade in VO2 max –aging and physical inactivity contribute Cartee - relative inc in VO2 max and ms resp capacity is similar old and young

10 Endurance Training Seals - 6 months low and high intensity training –30% mean increase in VO2 max –others 9-12 months - ~24 % inc Oxidative Capacity Table Suominen –20 min 3-5 X/week - 8 weeks yrs –inc 45% in Resp capacity –inc 12% in VO2 max Orlander - no inc - 12 weeks Meredith - 128% inc Ox cap, 20 in VO2 max -young 27 % inc in ox cap –** 45 minutes 3 X / week Coggan - fig 3.4A - 10 month program

11 Endurance Training Glycolytic capacity - minimal impact Capillarization –Coggan Fig 3.4 B –cap density inc 20 % –cap / fiber ratio inc 25% Fiber type alterations –Gollnick - 30 yrs old - 5 months –23 % inc in size of type I –no change in type II –no change in % type I –type II b to a shift Cogan - elderly - similar to above –changes that occur function of intensity and duration of stimulus

12 Prolonged Endurance Training Animal studies - prolonged wheel running or swimming training –for significant portion of life span –inc type I fiber mass, dec type II –20-40% inc in SDH, CS and B-HAD Human Studies –chronic intense endurance training in master athletes - reduce or eliminate decline in VO2 max over 10 yrs compared to performance matched younger athletes –same max (a-v)O2 difference –25-30% higher ox enzyme capacity –cap / fiber inc, cap / mm same

13 Resistance Training Regular resistance tx over sufficient time period –muscle hypertrophy, inc strength –alteration in body comp older individuals –table 3.3 Frontera - 12 weeks - 80 % 1RM –Inc 5 % / day (similar to young) Fig 3.6 a inc 100 % ext, 200 % flexors Fig 3.6 b - 11 % inc in Xsec area –inc type I and II ~30 % each –inc CS, Cap density, and VO2 max very old - 8 weeks high intensity –inc 174 % strength, 15 % X sec area