Training• Describe the differences between human

exercise and animal models of muscle plasticity

• Training-induced neural plasticity• Training strategies for modulating muscle

recruitment

Training programs (cardio)• P90X/Insanity (12 weeks)

– 30-60 min/day, continuous– Progressive (a little)– low load: no failure– 70-80% HRmax; 50-80% VO2max– Rotating muscle groups

• HIIT (High Intensity Interval)– 30 min / day, continuous– 40-50% VO2max with 30-60s anaerobic intervals

Training programs (strength)• HIT (High Intensity)

– 30-60 min / 2-3 day, short rests– 10-15 RM, recalibrated regularly, Consistent routine

• HST (Hypertrophy specific)– 60-90 min/ 2-3 day, intervals– Progressive– Max-load (2x15, 12, 10, 8, 5-rep max)– Consistent routine, emphasis on form

• Powerlift– 60-90 min/day, intervals– Progressive– High load (4x15, 12, 10, 8, 5-RM)– Rotating muscle groups , emphasis on completion

Training programs (research)• Endurance

– 30-60 min/day– 60-80% VO2max– Consistent routine (usu. cycling/running)

• Strength– 10-30 min /2-3 days– Single muscle group– 2-4 sets of 6-10 RM

• 8-16 weeks

Human variability• Single greatest challenge to human research

– Heterogenetic– Diet & activity variations– Drug/bioactive chemical

variations

• Sample size– n=5resolution ~2 S.D.– n=8 ~ 1.5 S.D.– N=12 ~1.2 S.D.

Satellite cells pre/post training split by magnitude of hypertrophy (Petrella & al., 2007)

Recruitment• Voluntary

– “Pacing” ie: projecting future activity requirement– Regulatory feedback

• Recurrent/Renshaw inhibition• GTO/force dependent inhibition• Central fatigue

– Skill

• Involuntary– Intensity– Frequency– Synchrony Power-endurance curve, Morton

& Hodgson, 1996

Recruitment during endurance ex• Pacing: activity increases at end• Temperature: central fatigue/stress reduces

activity

Tucker & al., 2004

15 °C35 ° C

15 °C35 ° C

Activation restricted to ~30% MVC

Training specificity• Kanchisa & Miyashita (1983)• Isokinetic training at

several speeds, 8 wk• Performance increases

only near training speed

Training Specificity• Kitai & Sale (1989)

– Isometric: 2x 10 “max”– 6 weeks

• Strength gain only at training angle

Training Specificity• Aagard & al., 1996

– Soccer players– Isokinetic @8 RM, 24 RM– “Loaded-kick” 16RM @ 0-400 deg/s

• High resistance improve isokinetic strength• No changes in kicking performance• “HST” vs “Power” training

– Form over performance– Break in form may allow ‘testing’ of control

pathways

Recruitment during controlled task

fMRI of calf before and after plantarflexion exercise (Yanagisaw & al., 2003)

fMRI of arm before & after maximal curl exercise (Adams & al., 1992)

Mechanical balance may limit the contribution of some muscles. Esp skilled motions

Electrical stimulation• Animal

– Cuff or hook electrodes on the nerve– Often anesthetized

• Human– Surface electrodes– Awake subjects– Pain threshold

fMRI of electrically stimulated quadriceps at tolerance limit ~50% activitation

Completeness of MVC• MVC: maximal voluntary

contraction• Interpolated twitch

– Add a single electrical pulse during MVC

Effect of an ‘extra’ impulse during an electrically evoked train (Belanger & McComas, 1981)

Effect of an electrical pulse during voluntary activation (Belanger & McComas, 1981)

Tension rise due to synchronous, max activationTension fall due to GTO, spindle feedback; antidromic collision

Completeness of MVC• Sensitive to posture• Sensitive to motion• Different among

muscles• Confused by synergists

Voluntary force (%MVC)

Endurance and interval• Burgomaster & al 2007

– 50 min continuous 60% VO2 cycling

– 5x30s max anaerobic in 30 min

• Equivalent metabolic gains• Similar signaling

– PGC-1a– CS– etc

Long/slow contractions increase recruitment

• MU fatigue reduces force capacity

• Fatigued units replaced by new

• Strategy for improving recruitment

Garland & al., 1994DeLuca & al., 1996

Sets and Reps• Berger (1962-1968)• 1-3 sets; 2-10 reps, 20 students/group• 12 weeks, max bench press

I II III

2 149±21 146±18 154±24

6 156±28 153±23 161±21

10 151±18 156±27 153±24

124±21

Intensity-protein synthesis• Kumar & al, 2009

– 40-90% 1-RM– Reps set to match force*time– Protein synthesis 1-2 hr post

• Can’t resolve anything– n=5– Trend is consistent

with intuition

Sets and reps• Stuart Philips’ lab (2010-2012)• Vary sets and load (reps to failure)

– Highest protein synthesis at lowest load– No difference in performance or hypertrophy

Mitchell & al., 2012Burd & al., 2010

mTOR/ERK siganling consistent with this

4x5 RM4x14 @24 RM4x24 @24 RM

Protein Synthesis Muscle Size

Detraining• Bickel & al., 2011

– 16 weeks Resistance training• 3x10-RM• 3/week

– 16 weeks Detraining• No exercise• 1x10-RM, 1/week (1/9)• 3x10-RM, 1/week (1/3)

• Age-dependent loss– 1/3 volume maintains young

Summary• Neural control is a big part of “strength”

– Coordination of multiple muscles– Complete recruitment of individual muscles

• Manipulating the nervous system is a big part of training– Practice to improve control– Fatigue to improve recruitment

• Lessons from animal models are hard to translate– Forcehypertrophy– Chronic activityendurance