Neuromuscular plasticity in quadriceps functions in response to training and how this might affect sprinting ability and kicking performance Per Aagaard 8th MuscleTech Network Workshop

1. and How this Might Affect Sprinting Ability
and Kicking Performance
Per Aagaard
Institute of sports science and clinical biomechanics,
University of Southern Denmark
paagaard@health.sdu.dk
8th MuscleTech Network Workshop · Barcelona October 3rd-4th 2016
Neuromuscular Plasticity in Quadriceps
Function in Response to Training

2. Brain
motor cortex
cerebellum
Spinal
cord
efferent
motorneurons
sensory
afferent
neurons
Muscle
Drawing modified
from Sale 1992
The Neuromuscular System
Neuromuscular function
- motor cortex, cerebellum
- spinal cord circuitry
- efferent motorneuron output
- sensory afferent feedback

3. Brain
motor cortex
cerebellum
Spinal
cord
efferent
motorneurons
sensory
afferent
neurons
Muscle
Drawing modified
from Sale 1992
The Neuromuscular System
Exercise & Training

Adaptive changes
in neuromuscular
function

 ECC strength,
 explosive strength
Neuromuscular function
- motor cortex, cerebellum
- spinal cord circuitry
- efferent motorneuron output
- sensory afferent feedback

4. Improvements in functional capacity:
 sports performance (i.e.  acc capacity),
 injury risk
Exercise
Sports
Performance

5. ain
tor cortex
ebellum
Spinal
cord
Muscle
Neuromuscular adaptations
related to...
- maximal ECCentric muscle strength
- explosive muscle strength (RFD)
Functional consequences for
Sprinting Ability and Kicking Performance
OUTLINE

6. can be evaluated by use of...
Muscle electromyography
(EMG) recording intramuscular & surface
Evoked spinal motoneuron responses:
H-reflex, V-wave recording
Transcranial magnetic / electrical stimulation
of cortical neurons and subcortical axons,
motor evoked responses (MEP)
Interpolated muscle twitch recording
superimposed during MVC



Changes in neuromuscularChanges in neuromuscular
functionfunction induced byinduced by
trainingtraining

-2500
2500
3000
-3000
-4000
4000
EMG VL
EMG VM
EMG RF
Time (msec)
0 1000 2000 3000 4000 5000
uVolt
uVolt
uVolt
Time (msec)
0 1000 2000 3000 4000 5000
Aagaard et al., J. Appl. Physiol. 2000
H
M
H
M
10 ms
2 mV
Changes in neuromuscular
function evoked by training,
disuse, injury, aging, etc

7. Neuromuscular Plasticity in
Quadriceps Function
Effects of resistance training on
maximal eccentric muscle strength)
position
Moment
EMG VL
EMG VM
EMG RF
oncentric contraction
ning
slow eccentric contraction
pre training

8. Types of
muscle contraction
Eccentric muscle contraction
muscle generating contractile force
while lengthening
Concentric muscle contraction
muscle generating contractile force
while shortening
Isometric muscle contraction
muscle generating contractile force
while maintaining constant length
Types ofTypes of
muscle contractionmuscle contraction
Eccentric muscle contraction
muscle generating contractile force
while lengthening
Concentric muscle contraction
muscle generating contractile force
while shortening
Isometric muscle contraction
muscle generating contractile force
while maintaining constant length
Eccentric
Concentric
Isometric

9. High eccentric strength in agonist muscles
… provides enhanced capacity to
decelerate (brake) movements
in very short time

- fast SSC actions
(i.e. rapid jump takeoff)
- fast changes in movement direction
(i.e. rapid side-cutting)
Why is ECCentric muscle strength important?

10. High eccentric strength in antagonist muscles
...provides enhanced capacity for antagonist muscles
to decelerate and stop movements at the end-ROM
 increased protection of joint ligaments (i.e. ACL)
and joint capsule structures
Aagaard et al., Am J Sports Med 1998
Why is ECCentric muscle strength important?
Hamstring muscles are exposed
to extreme lengthening changes and
high eccentric forces during sprint running
medial H: ST/SM muscle
lateral H: BFcl muscle
Simonsen et al. 1985
Muscle
lengths
EMG
on-off
periods

11. High level of ECCentric hamstring strength
 reduced incidence / full absence [very strong individuals]
of muscle strain injury in elite football players
Croisier et al, Am J Sports Med 36, 2008
(n=462 professional football players)
Why is ECCentric muscle strength important?
High eccentric knee flexor strength

12. From Aagaard & Thorstensson. Neuromuscular aspects of exercise: Adaptive responses evoked
by strength training, Textbook of Sports Medicine (Eds. Kjær et al) 2003
Velocity
ContractileForce/Strength
percent of Vmax
-40 -20 0 20 40 60 80 100
0
20
40
60
80
100
120
140
160
180
0
20
40
60
80
100
120
140
160
180
ArbitraryUnits
MuscleForce(isometric=100%)
isometric
CONcentricECCentric
Katz B, J. Physiol. 96, 1939
Contraction Speed
ContractileForce/Strength
percent of Vmax
0 20 40 60 80 100
0
20
40
60
80
100
120
140
160
180
Edman KAP, J. Physiol. 404, 1988
ArbitraryUnits
concentrictric
Katz B, J. Physiol. 96, 1939
Contraction Speed
ContractileForce/Strength
percent of Vmax
-20 0 20 40 60 80 100
0
20
40
60
80
100
120
140
160
180
0
20
40
60
80
100
120
140
160
180
Edman KAP, J. Physiol. 404, 1988
ArbitraryUnits
concentriceccentric
MuscleForce(isometric=100%)
The Force-Velocity relationship in skeletal muscle
recorded during maximal ECC and CON contraction
Isolated animal muscle
preparations

13. From Aagaard & Thorstensson. Neuromuscular aspects of exercise: Adaptive responses evoked
by strength training, Textbook of Sports Medicine (Eds. Kjær et al) 2003
Velocity
ContractileForce/Strength
percent of Vmax
-40 -20 0 20 40 60 80 100
0
20
40
60
80
100
120
140
160
180
0
20
40
60
80
100
120
140
160
180
ArbitraryUnits
MuscleForce(isometric=100%)
isometric
CONcentricECCentric
Katz B, J. Physiol. 96, 1939
Contraction Speed
ContractileForce/Strength
percent of Vmax
0 20 40 60 80 100
0
20
40
60
80
100
120
140
160
180
Edman KAP, J. Physiol. 404, 1988
ArbitraryUnits
concentrictric
Katz B, J. Physiol. 96, 1939
Contraction Speed
ContractileForce/Strength
percent of Vmax
-20 0 20 40 60 80 100
0
20
40
60
80
100
120
140
160
180
0
20
40
60
80
100
120
140
160
180
Edman KAP, J. Physiol. 404, 1988
ArbitraryUnits
concentriceccentric
MuscleForce(isometric=100%)
ECC >> CON (+50-100%)
The Force-Velocity relationship in skeletal muscle
recorded during maximal ECC and CON contraction
Isolated animal muscle
preparations

14. Contraction Speed
ContractileForce/Strength
percent of Vmax
-40 -20 0 20 40 60 80 100
0
20
40
60
80
100
120
140
160
180
0
20
40
60
80
100
120
140
160
180
ArbitraryUnits
concentriceccentric
From Aagaard & Thorstensson. Neuromuscular aspects of exercise: Adaptive responses evoked
by strength training, Textbook of Sports Medicine (Eds. Kjær et al) 2003
MuscleForce(isometric=100%)
isometric
CONcentricECCentric
Katz B, J. Physiol. 96, 1939
Contraction Speed
ContractileForce/Strength
percent of Vmax
-20 0 20 40 60 80 100
0
20
40
60
80
100
120
140
160
180
0
20
40
60
80
100
120
140
160
180
Edman KAP, J. Physiol. 404, 1988
ArbitraryUnits
concentriceccentric
MuscleForce(isometric=100%)
Intact human quadriceps muscle:
maximal voluntary activation
(Westing et al 1990)
Katz B, J. Physiol. 96, 1939
Contraction Speed
ContractileForce/Strength
percent of Vmax
0 20 40 60 80 100
0
20
40
60
80
100
120
140
160
180
Edman KAP, J. Physiol. 404, 1988
ArbitraryUnits
concentrictric
The Force-Velocity relationship in skeletal muscle
recorded during maximal ECC and CON contraction

15. Contraction Speed
ContractileForce/Strength
percent of Vmax
-40 -20 0 20 40 60 80 100
0
20
40
60
80
100
120
140
160
180
0
20
40
60
80
100
120
140
160
180
ArbitraryUnits
concentriceccentric
From Aagaard & Thorstensson. Neuromuscular aspects of exercise: Adaptive responses evoked
by strength training, Textbook of Sports Medicine (Eds. Kjær et al) 2003
MuscleForce(isometric=100%)
isometric
CONcentricECCentric
Katz B, J. Physiol. 96, 1939
Contraction Speed
ContractileForce/Strength
percent of Vmax
-20 0 20 40 60 80 100
0
20
40
60
80
100
120
140
160
180
0
20
40
60
80
100
120
140
160
180
Edman KAP, J. Physiol. 404, 1988
ArbitraryUnits
concentriceccentric
MuscleForce(isometric=100%)
Intact human quadriceps muscle:
electrical muscle stimulation
superimposed onto maximal
voluntary contraction
(Westing et al 1990)
Katz B, J. Physiol. 96, 1939
Contraction Speed
ContractileForce/Strength
percent of Vmax
0 20 40 60 80 100
0
20
40
60
80
100
120
140
160
180
Edman KAP, J. Physiol. 404, 1988
ArbitraryUnits
concentrictric
The Force-Velocity relationship in skeletal muscle
recorded during maximal ECC and CON contraction

16. Neural aspects of maximal ECC muscle contraction
- assessing neural inhibition in the neuromuscular system
Brain
motor cortex
cerebellum
Spinal
cord
Muscle
TEST SETUP
Isokinetic dynamometry

17. 100 Nm
-2500
2500
3000
-3000
-4000
4000
position
Moment
EMG VL
EMG VM
EMG RF
Time (msec)
0 1000 2000 3000 4000 5000
uVolt
uVolt
uVolt
Time (msec)
0 1000 2000 3000 4000 5000
Aagaard et al, J Appl Physiol 2000
90o
10o
90o
10o
Neuromuscular activity m. quadriceps
[untrained individual]
Calculating mean
filtered EMG amplitude (iEMG)
Calculating mean
filtered EMG amplitude (iEMG)
slow CONC contraction
pre training
slow ECC contraction
pre training

18. Aagaard et al, J Appl Physiol 2000
Untrained individuals
Reduced neuromuscular activity ( quadriceps EMG amplitude)
during maximal ECC contraction
100 Nm
-2500
2500
3000
-3000
-4000
4000
position
Moment
EMG VL
EMG VM
EMG RF
Time (msec)
0 1000 2000 3000 4000 5000
uVolt
uVolt
uVolt
Time (msec)
0 1000 2000 3000 4000 5000
position
Moment
EMG VL
EMG VM
EMG RF
sec)
0 4000 5000
Time (msec)
0 1000 2000 3000 4000 5000
*
*
**
*
* *
*
*
*
percent
EMG RF
EMG VM
EMG VL
Knee angular velocity
60
70
80
90
100
Percent
60
70
80
90
100
Percent
60
70
80
90
100
Percent
concentriceccentric
100
120
140
160
180
200
240
Percent
( o s-1 )
30-30-240
force moment
quadriceps
percent
percent
percent

19. Average quadriceps EMG and strength
Aagaard et al, J Appl Physiol 2000
Untrained individuals
Reduced neuromuscular activity ( quadriceps EMG amplitude)
during maximal ECC contraction
**
*
*
*
*
mean EMG
Quadriceps
Knee angular velocity
60
70
80
90
100
Percent
concentriceccentric
100
120
140
160
180
200
240
Percent
( o s-1 )
30-30-240
Quadriceps
force moment
(percent)
(percent)
* *
*
100 Nm
-2500
2500
3000
-3000
-4000
4000
position
Moment
EMG VL
EMG VM
EMG RF
Time (msec)
0 1000 2000 3000 4000 5000
uVolt
uVolt
uVolt
Time (msec)
0 1000 2000 3000 4000 5000
fast ECC slow slow CONC fast
position
Moment
EMG VL
EMG VM
EMG RF
sec)
0 4000 5000
Time (msec)
0 1000 2000 3000 4000 5000

20. Neuromuscular activity appears to be reduced during
maximal voluntary ECCentric muscle contraction, indicating
that motoneuron activation is inhibited (untrained subjects)
Aagaard 2000, Andersen 2005, McHugh 2002, Komi 2000, Kellis &
Baltzopoulos 1998, Higbie 1996, Amiridis 1996, Seger & Thorstensson 1994,
Bobbert & Harlaard 1992, Westing 1991, Tesch 1990, Eloranta & Komi 1980,
Duclay & Martin 2005, Duclay et al 2008, Gruber 2009, Abbruzzese 1994,
Sekiguchi 2001 & 2003, Duclay et al 2011
 surface EMG amplitude (iEMG, aEMG)
 evoked motorneurone response (H-reflex)
 MEP,  CMEP responses (TMS, CMS)
[unchanged or elevated MEP/CMEP ratio]
sition
oment
MG VL
MG VM
MG RF
Time (msec)
0 1000 2000 3000 4000 5000
Inhibited neuromuscular activity during
maximal ECCentric muscle contraction
H
M
H
M
10 ms
2 mV

21. Neuromuscular activity during ECCentric muscle contractions
Effects of conventional resistance training?

22. MomentofForce(Nm)
knee angular velocity ( o
s-1
)
-120 24012030-30-240
0
100
200
300
400
velocity of training
50o
peak
*
**
*
**
**
**
eccentric concentric
HR group (n=7)
*
Quadriceps muscle strength, Elite football players
Before and after 12 weeks strength training
Aagaard et al, Acta Physiol Scand 1996
Heavy-resistance
strength training
(8 RM loads)
Effects of strength training on maximal
eccentric and concentric muscle strength 

23. Conventionel heavy-resistance strength training

 ECC strength,  CONC strength
Aagaard 2000, Andersen 2005, Seger 1998, Aagaard 1996, Hortobagyi 1996,
Timmins 2016, Higbie 1996, Colliander & Tesch 1990, Narici 1989, Komi & Buskirk 1972
No changes in maximal ECCentric muscle strength
following low-resistance strength training
Aagaard 1996, Duncan 1989, Takarada 2000, Holm Aagaard et al 2008
Effects of heavy-resistance strength training
on maximal ECC muscle strength

24. Aagaard et al, J Appl Physiol 2000
**
*
*
*
*
mean EMG
Quadriceps
Knee angular velocity
60
70
80
90
100
Percent
concentriceccentric
100
120
140
160
180
200
240
Percent
( o s-1 )
30-30-240
Quadriceps
force moment
(percent)
(percent)
* *
*
**
*
*
*
*
mean EMG
Quadriceps
Knee angular velocity
60
70
80
90
100
Percent
concentriceccentric
100
120
140
160
180
200
240
Percent
( o s-1 )
30-30-240
Quadriceps
force moment
(percent)
(percent)
* *
*
Post
Pre
Heavy-resistance strength training (14 wks)
 Reduced suppression in quadriceps EMG amplitude
during ECC contraction   ECCentric muscle strength
PRE TRAINING POST TRAINING
Average quadriceps EMG and strengthAverage quadriceps EMG and strength

25. Andersen LL, Andersen JL, Magnusson SP, Aagaard P 2005
Neuromuscular activity during
maximal eccentric muscle contraction
- effects of resistance training
Gain in maximal ECC
muscle strength
strongly related to
the improvement in
neuromuscular activity
(r=0.89, p < 0.001)
Andersen, Aagaard et al. 2005
 slow ecc norm EMG
0 20 40 60 80 100 120 140
sloweccmomentofforce
0
20
40
60
80
100
120
R2
= 0.77, p<0.001
 % ECC norm EMG at 30o/s
%ECCTorqueat30o/
r = 0.89, p<0.001

26. Effects of heavy-resistance strength training:
- reduced inhibition in motorneuron activation
during ECC contraction   neuromuscular drive
  ECC muscle force production
Neuromuscular activity during
maximal ECCentric muscle contraction
Effects of conventional resistance training

27. Functional consequences:
- faster SSC muscle actions
-  Power in SSC movements
- faster decelerations (sidecutting etc)
-  ECC antagonist muscle strength
(joint protection, reduced risk of injury)
Neuromuscular activity during
maximal ECCentric muscle contraction
Effects of conventional resistance training
Effects of heavy-resistance strength training:
- reduced inhibition in motorneuron activation
during ECC contraction   neuromuscular drive
  ECC muscle force production

28. subj LN
RF EMG
VM EMG
VL EMG
Force MomentNm
uVolts
uVolts
Time ( miliseconds )
0
100
200
300
-1500
1500
-1200
1200
-400 0 400 800 1200 1600 2000 2400 2800
-1000
1000
uVolts
Fig.1A
art14F1a.jnb
Time (milliseconds)
Aagaard et al. 2002
Force
Moment
VL EMG
VM EMG
RF EMG
Neuromuscular Plasticity in
Quadriceps Function
Effects of resistance training on explosive muscle
strength / Rapid Force Capacity (RFD))

29. Neuromuscular Plasticity in
Quadriceps Function
Effects of resistance training on explosive muscle
strength / Rapid Force Capacity (RFD))
subj LN
RF EMG
VM EMG
VL EMG
Force MomentNm
uVolts
uVolts
Time ( miliseconds )
0
100
200
300
-1500
1500
-1200
1200
-400 0 400 800 1200 1600 2000 2400 2800
-1000
1000
uVolts
Fig.1A
art14F1a.jnb
Time (milliseconds)
Aagaard et al. 2002
Force
Moment
VL EMG
VM EMG
RF EMG
Why is RFD important ?

30. Ground contact times…
110 - 160 msec in long jump
180 - 220 msec in high jump
80 - 120 msec in sprint running
Luhtanen & Komi 1979, Dapena & Chung 1988,
Zatsiorsky 1995, Kuitunen et al. 2002
Time to reach peak force production in
human skeletal muscle…
300 - 500 msec
Sukop & Nelson 1974, Thorstensson et al. 1976,
Aagaard et al. 2002
TIME IS LIMITED...

31. 1000
2000
3000
4000
5000
0
0.20 0.4 0.6 0.8
Time (seconds)
Force(N)
RFD =
Force / Time
Force
Time
max Force
Rate of Force Development (RFD)
Aagaard et al, J Appl Physiol 2002
1000
2000
3000
4000
5000
0
0.20 0.4 0.6 0.8
Force(N)
RFD =RFD =
Force / Time
Force
Time
max Force
m. quadriceps
femoris
Maximal Explosive Muscle Strength
‘Rapid Force Capacity’

32. Contractile RFD
Assessed by isokinetic dynamometry

33. RFD
= Force / Time
= slope of Force-time curve

34. RFD = Force / Time
peak tangential slope

35. RFD = Force / Time
mean tangential slope 0-30 ms

36. RFD = Force / Time
mean tangential slope 0-50 ms

37. RFD = Force / Time
mean tangential slope 0-100 ms

38. RFD = Force / Time
mean tangential slope 0-200 ms

39. Maximal isometric quadriceps contraction, static knee extension
Aagaard et al, J Appl Physiol 2002
-1000 -500 0 500 1000 1500 2000 2500 3000
-800
-400
0
400
800
0
400
800
lowpass filtered
raw EMG signal
Time (miliseconds)
uVolt
rectified EMG signal
uVolt
highpass filtered
subj LN
RF EMG
VM EMG
VL EMG
Force MomentNm
uVolts
uVolts
Time ( miliseconds )
0
100
200
300
-1500
1500
-1200
1200
-400 0 400 800 1200 1600 2000 2400 2800
-1000
1000
uVolts
Fig.1A
art14F1a.jnb
Time (milliseconds)
Aagaard et al. 2002
Force
Moment
VL EMG
VM EMG
RF EMG
subj LN
RF EMG
VM EMG
VL EMG
Force MomentNm
uVolts
uVolts
Time ( miliseconds )
0
100
200
300
-1500
1500
-1200
1200
-400 0 400 800 1200 1600 2000 2400 2800
-1000
1000
uVolts
Fig.1A
art14F1a.jnb
Time (milliseconds)
Aagaard et al. 2002
Force
Moment
VL EMG
VM EMG
RF EMG
Isometric Quadriceps
knee extensor moment signal
Rectified EMG signal (grey)
lowpass filtered EMG signal
raw EMG signal
highpass filtered
VL muscle
RFD = Moment/time
Recording of neuromuscular activity and RFD

40. Del Balso & Cafarelli, J Appl Physiol 2007 [soleus muscle]
Influence of neuromuscular activity on RFD
Rapid force capacity (RFD) is strongly influenced by the
magnitude of neuromuscular activity at onset of contraction
RFD
iEMG
r = 0.91
p<0.001

41. Effects of resistance training
Training-induced
changes in RFD
and neuromuscular
activity
position
Moment
EMG VL
EMG VM
ction slow eccentric contraction
pre training
al drivem. quadriceps
Neuromuscular Plasticity in Quadriceps function
Contractile Rate of Force Development (RFD)

42. Pre and post 14 wks of heavy-resistance strength training
RFD Contractile Rate of Force Development
Assessed during maximal isometric quadriceps contraction
ForceMoment
(Nm)
(miliseconds)Time
-100 0 100 200 300 400
0
50
100
150
200
250
300
Pre training
Post training
MVC post
339 Nm
MVC pre
291 Nm
ForceMoment
(Nm)
(miliseconds)Time
-100 0 100 200 300 400
0
50
100
150
200
250
300
Pre training
Post training
Aagaard et al, J Appl Physiol 2002

43. Pre to post training differences: * p < 0.05, ** p < 0.01
error bars: SEM
Nm/sec
#
* **
peak msec2001005030
0
500
1000
1500
2000
2500
3000
3500
#
#
*
*
*
*
**
RFDRFD Contractile Rate of Force DevelopmentContractile Rate of Force Development
Aagaard et al.
J. Appl. Physiol. 2002
Pre and post 14 wks of heavy-resistance strength training
Pre to post training differences: * p < 0.05, ** p < 0.01
RFD Contractile Rate of Force Development
Assessed during maximal isometric quadriceps contraction
Pre and post 14 wks of heavy-resistance strength training
Aagaard et al, J Appl Physiol 2002

44. Neuromuscular activity and rapid force capacity (RFD)
Moment-time curve and filtered EMG signals at -200 to +600 ms
Nm
uVolts
uVolts
Time ( milliseconds )
0
100
200
0
800
0
800
-200 0 200 400 600
0
600
uVolts
Force
Moment
VL EMG
VM EMG
RF EMG
time of onset of force
-75 ms
onset of EMG
integration
Aagaard et al, J Appl Physiol 2002

45. Pre to post training differences: * p < 0.05, ** p < 0.01
(uVolt)
100 miliseconds50 ms30 ms
**
**
**
**
*
integrated for
RF
VL
VM
0
50
100
150
200
250
300
350
400
450
meanEMGamplitude,MAV
*
uVolt
VL
VM
RF
Pre training
Post training
VL vastus lateralis
Neuromuscular activity and rapid force capacity (RFD)
quadriceps mean integrated EMG
divided by integration time (MAV)
Aagaard et al, J Appl Physiol 2002

46. Pre to post training differences: * p < 0.05, ** p < 0.01
RF
(uVolt)
100 miliseconds50 ms30 ms
**
**
**
**
*
integrated for
RF
VL
VM
0
50
100
150
200
250
300
350
400
450
meanEMGamplitude,MAV
*
uVolt
*
*
RF rectus femoris
Neuromuscular activity and rapid force capacity (RFD)
quadriceps mean integrated EMG
divided by integration time (MAV)Pre training
Post training
Aagaard et al, J Appl Physiol 2002

47. Pre to post training differences: * p < 0.05, ** p < 0.01
RF
(uVolt)
100 miliseconds50 ms30 ms
**
**
**
**
*
integrated for
RF
VL
VM
0
50
100
150
200
250
300
350
400
450
meanEMGamplitude,MAV
*
uVolt
VM vastus medialis
*
Neuromuscular activity and rapid force capacity (RFD)
quadriceps mean integrated EMG
divided by integration time (MAV)Pre training
Post training
Aagaard et al, J Appl Physiol 2002

48. Pre to post training differences: * p < 0.05, ** p < 0.01
(uVolt/s)
75 miliseconds50 ms30 ms
*
derived over
RF
VL
VM
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
**
**
**
RateofEMGrise,RER
*
*
**
VL
VM
RF
Neuromuscular activity and rapid force capacity (RFD)
Rate of EMG rise (EMG/t)
Pre training
Post training
100 mV
200 ms
Aagaard et al, J Appl Physiol 2002

49. Heavy-resistance strength training
Increased neuromuscular drive
...in initial 200 msec of contraction
Increased maximal Rate of Force Development (RFD)
100 Nm
-2500
2500
3000
-3000
-4000
4000
position
Moment
EMG VL
EMG VM
EMG RF
Time (msec)
0 1000 2000 3000 4000 5000
uVolt
uVolt
uVolt
Time (msec)
0 1000 2000 3000 4000 5000
slow concentric contraction
pre training
slow eccentric contraction
pre training
Neural drivem. quadriceps
Aagaard et al., J. Appl. Physiol. 2000
1000
2000
3000
4000
5000
0
0.20 0.4 0.6 0.8
RFDRFD ==
Force / Time
Force
Time
max Force
Training induced changes in
rapid muscle force (RFD)

50. Heavy-resistance strength training
Increased neuromuscular drive
...in initial 200 msec of contraction
Increased maximal Rate of Force Development (RFD)
100 Nm
-2500
2500
3000
-3000
-4000
4000
position
Moment
EMG VL
EMG VM
EMG RF
Time (msec)
0 1000 2000 3000 4000 5000
uVolt
uVolt
uVolt
Time (msec)
0 1000 2000 3000 4000 5000
slow concentric contraction
pre training
slow eccentric contraction
pre training
Neural drivem. quadriceps
Aagaard et al., J. Appl. Physiol. 2000
Increased RFD along with increases in iEMG
Häkkinen & Komi 1986, Häkkinen 1985, 1998, Van Cutsem 1998, Barry 2005
Aagaard 2002, Suetta 2005, Del Balso & Cafarelli 2007, Vila-Chã 2010, Tillin Folland 2014
Elevated rate of EMG rise
Aagaard 2002, Barry 2005, Del Balso & Cafarelli 2007, Blazevich 2008


Training induced changes in
rapid muscle force (RFD)

51. Heavy-resistance strength training
Increased neuromuscular drive
...in initial 200 msec of contraction
Increased maximal Rate of Force Development (RFD)
100 Nm
-2500
2500
3000
-3000
-4000
4000
position
Moment
EMG VL
EMG VM
EMG RF
Time (msec)
0 1000 2000 3000 4000 5000
uVolt
uVolt
uVolt
Time (msec)
0 1000 2000 3000 4000 5000
slow concentric contraction
pre training
slow eccentric contraction
pre training
Neural drivem. quadriceps
Aagaard et al., J. Appl. Physiol. 2000
Functional consequences:
- enhanced acceleration
- faster movement speeds
- elevated muscle force and muscle
power during fast movements
- more rapid movement execution
Training induced changes in
rapid muscle force (RFD)

52. Heavy-resistance strength training
Increased neuromuscular drive
...in initial 200 msec of contraction
Increased maximal Rate of Force Development (RFD)
100 Nm
-2500
2500
3000
-3000
-4000
4000
position
Moment
EMG VL
EMG VM
EMG RF
Time (msec)
0 1000 2000 3000 4000 5000
uVolt
uVolt
uVolt
Time (msec)
0 1000 2000 3000 4000 5000
slow concentric contraction
pre training
slow eccentric contraction
pre training
Neural drivem. quadriceps
Aagaard et al., J. Appl. Physiol. 2000
Training induced changes in
rapid muscle force (RFD)
???
Specific
adaptation
mechanisms

53. Heavy-resistance strength training
Increased neuromuscular drive
...in initial 200 msec of contraction
Increased maximal Rate of Force Development (RFD)
100 Nm
-2500
2500
3000
-3000
-4000
4000
position
Moment
EMG VL
EMG VM
EMG RF
Time (msec)
0 1000 2000 3000 4000 5000
uVolt
uVolt
uVolt
Time (msec)
0 1000 2000 3000 4000 5000
slow concentric contraction
pre training
slow eccentric contraction
pre training
Neural drivem. quadriceps
Aagaard et al., J. Appl. Physiol. 2000
Training induced changes in
rapid muscle force (RFD)
 maximal firing frequency of individual
motorneurons (motor units)
Van Cutsem 1998, Kamen & Knight 2004, Christie & Kamen 2010
 number of ‘discharge doublets’ in the
motorneuron (motor unit) firing pattern
Van Cutsem 1998
Potential
adaptation
mechanisms

54. Increased motorneuron
discharge rates following strength training!
post training
pre training
0
50
100
150
200
0
50
100
150
200
Based on data from
Van Cutsem, J. Physiol. 1998
Post > Pre, P < 0.001
MotorUnit
firingrate(Hz)
I. II. III.
Interspike intervals
I. II. III.
*
*
* *
Aagaard, Exerc. Sports Sci. Reviews 2003
- data adapted from Van Cutsem et al, J Physiol 1998
10 ms
2.4 ms
4.2 ms
4.8 ms
Changes in RFD and Motorneuron discharge rates
following 12 wks ballistic resistance training [TA muscle, 40-50% 1RM]

55. Increased motorneuron
discharge rates following strength training!
post training
pre training
0
50
100
150
200
0
50
100
150
200
Based on data from
Van Cutsem, J. Physiol. 1998
Post > Pre, P < 0.001
MotorUnit
firingrate(Hz)
I. II. III.
Interspike intervals
I. II. III.
*
*
* *
Aagaard, Exerc. Sports Sci. Reviews 2003
- data adapted from Van Cutsem et al, J Physiol 1998
10 ms
2.4 ms
4.2 ms
4.8 ms
Changes in RFD and Motorneuron discharge rates
following 12 wks ballistic resistance training [TA muscle, 40-50% 1RM]
Maximal motorneuron firing frequency
increased by 60-80% following 12 wk
ballistic-type resistance training
 increased contractile RFD

57. and How this Might Affect Sprinting Ability
and Kicking Performance
Neuromuscular Plasticity in Quadriceps Function
in Response to Training

58. Bret et al, J Sports Med Phys Fitness 2002
n=19 male elite track & field sprinters, French regional to national level
Relationship between SPRINT capacity and
maximal lower limb muscle strength in track & field sprinters
Average 100-m speed vs Maximal muscle strength
26 28 30 32 34 36 38
Leg extensor strength
concentric half-squats (N/kg Bw)
Runningspeed
mean100-maverage(m/s)
9.4
9.0
8.6
8.2
7.8
r = 0.74, p<0.001

59. 1-RM Squat strength
Relationship between SPRINT capacity and
maximal lower limb muscle strength in football players
Short sprint (acceleration) vs Maximal muscle strength
Acceleration capacity
10-m sprint
r = 0.94, p<0.001
Wisløff et al, Br J Sports Med 2004
n=17 male elite football players, international level

60. Wisløff et al, Br J Sports Med 2004
n=17 male elite football players, international level
1-RM Squat strength
r = 0.71, p<0.01
Maximum speed capacity
30-m sprint
Relationship between SPRINT capacity and
maximal lower limb muscle strength in football players
Long sprint (max speed) vs Maximal muscle strength

61. Relationship between vertical JUMP capacity
and maximal lower limb muscle strength in football players
Vertical jump height (CMJ)
1-RM Squat strength
Wisløff et al, Br J Sports Med 2004
n=17 male elite football players, international level
r = 0.78, p<0.05

62. Tillin, Folland et al,
J Sports Sci 2013 [static squat]
Short 5-m sprint
times (<1 s)
(n=10)
Long 5-m
sprint times (≥1 s)
(n=8)
Rapid force capacity - Rate of Force Development (RFD)
Effects of RFD on acceleration capacity
Elite rugby players (n=18)
Isometric leg extensor RFD
measured at 0-50-250 ms

63. Tillin, Folland et al,
J Sports Sci 2013 [static squat]
Elite rugby players (n=18)
Isometric leg extensor RFD
measured at 0-50-250 ms
indirect measure of
Relative RFD at 100 ms
5-m sprint time
Rapid force capacity - Rate of Force Development (RFD)
Effects of RFD on acceleration capacity

64. Helgerud, Rodas et al, Int J Sports Med 2011
n=21 male elite football players, UEFA Champions’ League
Half-squat resistance training with 4-RM loads in 4 reps × 4 sets
performed concurrently with regular soccer training,
Twice a week for 8 weeks (16 sessions)
+52% +47% +5% +3% +2%
Influence of resistance training on sprint capacity in football...

65. Strength training: 4 sets of 6-RM of high-pull, jump squat, bench press, back half squat, and chin-up
exercises. High intensity interval training: 16 intervals each of 15-s sprints at 120% of individual maximal
aerobic speed. For 8 wks, twice per wk (16 sessions in total)
Influence of resistance training on sprint capacity in football...

66. Strength training: 4 sets of 6-RM of high-pull, jump squat, bench press, back half squat, and chin-up
exercises. High intensity interval training: 16 intervals each of 15-s sprints at 120% of individual maximal
aerobic speed. For 8 wks, twice per wk (16 sessions in total)
vertical CMJ height 10-m sprint time 30-m sprint time
Relative changes with training
4%
5.5% 3%
Influence of resistance training on sprint capacity in football...

67. Effects of resistance training on
kicking performance in elite football players
Maximal ball release speed pre-post 12 wks of resistance training
Aagaard et al, Acta Physiol Scand1996
n=22 male elite football players
HR: Heavy resistance 4 sets, 8 reps (8 RM)
LR: Low resistance 4 sets, 24 reps (24 RM)
LK: Loaded kicking movments 4 sets, 16 reps (16 RM)
CO: Control group; No strength training
70.0
75.0
80.0
85.0
90.0
95.0
100.0
105.0
110.0
115.0
120.0
HR LR LK CO
Velocity(kmperhr)
Kicking performance
Before training
After Training
70.0
75.0
80.0
85.0
90.0
95.0
100.0
105.0
110.0
115.0
120.0
HR LR LK CO
Velocity(kmperhr)
Kicking performance
Before training
After Training
ce
Before training
After Training

68. Aagaard et al, Acta Physiol Scand1996
n=22 male elite football players
HR: Heavy resistance 4 sets, 8 reps (8 RM)
LR: Low resistance 4 sets, 24 reps (24 RM)
LK: Loaded kicking movments 4 sets, 16 reps (16 RM)
CO: Control group; No strength training
70.0
75.0
80.0
85.0
90.0
95.0
100.0
105.0
110.0
115.0
120.0
HR LR LK CO
Velocity(kmperhr)
Kicking performance
Before training
After Training
70.0
75.0
80.0
85.0
90.0
95.0
100.0
105.0
110.0
115.0
120.0
HR LR LK CO
Velocity(kmperhr)
Kicking performance
Before training
After Training
ce
Before training
After Training
No effect of 12 wks of resistance training
(slow-heavy, fast-power, or functional exercise)
on maximal ball kicking speed ...
Effects of resistance training on
kicking performance in elite football players
Maximal ball release speed pre-post 12 wks of resistance training

69. SUMMARY
Neuromuscular Plasticity in
Quadriceps Function in Response to Training

70. Neuromuscular Plasticity in Quadriceps Function
Adaptive changes in rapid force capacity (RFD) &
ECC muscle strength induced by resistance training
SUMMARY

on
nt
VL
VM
RF
Time (msec)
0 1000 2000 3000 4000 5000
Aagaard et al., J. Appl. Physiol. 2000
 motorneuron inhibition during ECC contraction   ECC strength
Aagaard 2000, Andersen 2005, Duclay 2008
►

71. Neuromuscular Plasticity in Quadriceps Function
Adaptive changes in rapid force capacity (RFD) &
ECC muscle strength induced by resistance training
SUMMARY

on
nt
VL
VM
RF
Time (msec)
0 1000 2000 3000 4000 5000
Aagaard et al., J. Appl. Physiol. 2000
 motorneuron inhibition during ECC contraction   ECC strength
Aagaard 2000, Andersen 2005, Duclay 2008
 Neuromuscular activity at force onset (0-200 ms)   RFD
Aagaard 2002, Barry 2005, Del Balso & Cafarelli 2007, Schmidtbleicher & Buehrle 1987
►
►
Nm
uVolts
uVolts
Time ( milliseconds )
0
100
200
0
800
0
800
-200 0 200 400 600
0
600
uVolts
Force
Moment
VL EMG
VM EMG
RF EMG

72. Neuromuscular Plasticity in Quadriceps Function
Adaptive changes in rapid force capacity (RFD) &
ECC muscle strength induced by resistance training
SUMMARY

on
nt
VL
VM
RF
Time (msec)
0 1000 2000 3000 4000 5000
Aagaard et al., J. Appl. Physiol. 2000
►
►
►
Nm
uVolts
uVolts
Time ( milliseconds )
0
100
200
0
800
0
800
-200 0 200 400 600
0
600
uVolts
Nm
uVolts
uVolts
0
100
200
0
800
0
800
600
uVolts
Nm
uVolts
uVolts
0
100
200
0
800
0
800
-200 0 200 400 600
0
600
uVolts
Force
Moment
VL EMG
VM EMG
RF EMG
Force
Moment
VL EMG
VM EMG
 motorneuron inhibition during ECC contraction   ECC strength
Aagaard 2000, Andersen 2005, Duclay 2008
 Neuromuscular activity at force onset (0-200 ms)   RFD
Aagaard 2002, Barry 2005, Del Balso & Cafarelli 2007, Schmidtbleicher & Buehrle 1987
 Rate of EMG rise (RER)   Rate of Force development (RFD)
Aagaard 2002, Barry 2005, Del Balso & Cafarelli 2007, Blazevich 2008

73. Neuromuscular Plasticity in Quadriceps Function
Adaptive changes in rapid force capacity (RFD) &
ECC muscle strength induced by resistance training
SUMMARY

on
nt
VL
VM
RF
Time (msec)
0 1000 2000 3000 4000 5000
Aagaard et al., J. Appl. Physiol. 2000
 motorneuron inhibition during ECC contraction   ECC strength
Aagaard 2000, Andersen 2005, Duclay 2008
 Neuromuscular activity at force onset (0-200 ms)   RFD
Aagaard 2002, Barry 2005, Del Balso & Cafarelli 2007, Schmidtbleicher & Buehrle 1987
 Rate of EMG rise (RER)   Rate of Force development (RFD)
Aagaard 2002, Barry 2005, Del Balso & Cafarelli 2007, Blazevich 2008
 Maximal motorneuron firing frequency   RFD
Van Cutsem 1998, Patten et al 2001, Kamen & Knight 2004, Christie & Kamen 2010
motorneuron firing:  incidence of discharge ‘doublets’   RFD
Van Cutsem 1998
►
►
►
►
►

74. ... And How this Might Affect Sprinting Ability and Kicking Performance
SUMMARY

on
nt
VL
VM
RF
Time (msec)
0 1000 2000 3000 4000 5000
Aagaard et al., J. Appl. Physiol. 2000
Neuromuscular Plasticity in Quadriceps Function
Adaptive changes in rapid force capacity (RFD) &
ECC muscle strength induced by resistance training

75. ... And How this Might Affect Sprinting Ability and Kicking Performance
Sprinting ability, including long sprint and short sprint
(acceleration capacity) can be increased in high-level football
players by means of heavy-resistance strength training
►
SUMMARY

on
nt
VL
VM
RF
Time (msec)
0 1000 2000 3000 4000 5000
Aagaard et al., J. Appl. Physiol. 2000
Neuromuscular Plasticity in Quadriceps Function
Adaptive changes in rapid force capacity (RFD) &
ECC muscle strength induced by resistance training

76. ... And How this Might Affect Sprinting Ability and Kicking Performance
Sprinting ability, including long sprint and short sprint
(acceleration capacity) can be increased in high-level football
players by means of heavy-resistance strength training
Kicking performance measured as maximal ball flight speed
does not seem to be positively affected by resistance training,
at least not when performed for short periods of time (8-12 wks)
Kicking actions may be performed faster, due to RFD ((?))
►
►
►
SUMMARY

on
nt
VL
VM
RF
Time (msec)
0 1000 2000 3000 4000 5000
Aagaard et al., J. Appl. Physiol. 2000
Neuromuscular Plasticity in Quadriceps Function
Adaptive changes in rapid force capacity (RFD) &
ECC muscle strength induced by resistance training

77. Bangsbo & Andersen,
Power Training in Football 2013
Physiological changes associated with
strength/power training in football players

78. Bangsbo & Andersen,
Power Training in Football 2013
Physiological changes associated with
strength/power training in football players
?

79. Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark;
▼
Institute of Sports Medicine Copenhagen, University of Copenhagen
Michael Kjær
Peter Magnusson
Charlotte Suetta
Mette Zebis
Ulrik Frandsen
Peter Krustrup
Lars Hvid
Jakob Nielsen
Jesper L. Andersen
Poul Dyhre-Povlsen
Erik B. Simonsen
Tony Blazevich
Lars L Andersen
Markus Jakobsen
Emil Sundstrup
Anders Jørgensen
Acknowledgements

81. "... The analysis comprised 510 subjects and 85 effect sizes
(ESs), nested with 26 experimental and 11 control groups
and 15 studies ..."
"... Results: There is a transfer between increases in lower
body strength and sprint performance as indicated by a
very large significant correlation (r = -0.77; p = 0.0001)
between squat strength ES and sprint ES ..."

82. Slow-type jumper
(Landing type drop jump)
Fast-type jumper
(Bouncing type drop jump)
Tcontact = 361 ms 272 ms
Dyhre-Poulsen et al, J Physiol 437, 1991
Motorneuron excitability and ECC performance
Elite (National Team) volleyball players - Drop Jump test

83. Brain
motor cortex
cerebellum
Spinal
cord
efferent
motor neurons
sensory
afferent
neurons
Muscle
Drawing modified from Sale 1992
Enhanced
descending
motor drive from
higher CNS centres
Increased
spinal motoneuron
excitability
Resistance trainingResistance training  improved neuromuscular functionimproved neuromuscular function
Aagaard P. Exercise and Sports Science Reviews 31, 2003
 maximal muscle strength
 rapid force capacity
 maximal muscle power
 eccentric muscle strength
Nerve impulses 
Nerve impulses 
explosive strength (RFD)

84. Neural and muscular adaptations with resistance training
Morphological *
6-12 RM loads adaptation  Maximal muscle strength
“muscle volume training” mechanisms
 Explosive muscle strength
(Rate of Force Development)
Neural
1-8 RM loads adaptation  Eccentric muscle strength
“explosive type training” mechanisms **
*  muscle cross-sectional area (CSA) Narici 1989, Aagaard 2001
 CSA, type II muscle fibres (type II MHC isoforms) Andersen & Aagaard 2000, Aagaard 2001
changes in muscle architecture (fibre pennation) Aagaard 2001, Seynnes 2007, Blazevich 2007
**  neural drive to muscle fibres ( iEMG) Narici 1989, Schmidtbleicher 1987, Aagaard 2000, 2002
 motoneuron excitability,  supraspinal motor drive Aagaard 2002, Del Balso & Cafarelli 2007
 EMG depression in ECC contraction Aagaard 2000, Andersen 2005
Aagaard, Exercise Sports Science Reviews 2003

88. Improvements in functional capacity:
 performance in activities of daily living
(horizontal gait speed, stair walking, chair rising)
Neuromuscular function
- motor cortex, cerebellum
- spinal cord circuitry
- sensory afferent feedback
- efferent motorneuron output
Training

Adaptive changes
in neuromuscular
function

 ECC strength,
 explosive strength

90. Effects of resistance training
Is RFD also improved during dynamic
SSC muscle actions???
Neuromuscular Plasticity in Quadriceps function
Contractile Rate of Force Development (RFD)

91. Force Plate Methodology
Analysis of leg extension force (GRF)
and power during maximal jumping
Body center
of mass (BCM)
Force plate
Force plate
amplifier
Data acquisition:
Sampling: 1000 samples/s
Acquisition interval: 5 s
12 bit
Sampling card
Vertical ground reaction
forces of body center of
mass
Vertical ground
reaction force
GRF (Fz)
Force plate
Force plate
amplifier
Data acquisition:
Sampling: 1000 samples/s
Acquisition interval: 5 s
12 bit
Sampling card
Vertical ground reaction
forces of body center of
mass
Force plate
Force plate
amplifier
Data acquisition:
Sampling: 1000 samples/s
Acquisition interval: 5 s
12 bit
Sampling card
Vertical ground reaction
forces of body center of
mass
Force plate
Force plate
amplifier
Data acquisition:
Sampling: 1000 samples/s
Acquisition interval: 5 s
12 bit
Sampling card
Vertical ground reaction
forces of body center of
mass
Force plate
Force plate
amplifier
Data acquisition:
Sampling: 1000 samples/s
Acquisition interval: 5 s
12 bit
Sampling card
Vertical ground reaction
forces of body center of
mass
Force plate
Force plate
amplifier
Data acquisition:
Sampling: 1000 samples/s
Acquisition interval: 5 s
12 bit
Sampling card
Vertical ground reaction
forces of body center of
mass
Force plate
Force plate
amplifier
Data acquisition:
Sampling: 1000 samples/s
Acquisition interval: 5 s
12 bit
Sampling card
Vertical ground reaction
forces of body center of
mass
Force plate
Force plate
amplifier
Data acquisition:
Sampling: 1000 samples/s
Acquisition interval: 5 s
12 bit
Sampling card
Vertical ground reaction
forces of body center of
mass
Force plate
Force plate
amplifier
Data acquisition:
Sampling: 1000 samples/s
Acquisition interval: 5 s
12 bit
Sampling card
Vertical ground reaction
forces of body center of
mass
-1000
0
1000
2000
0 1000 2000 3000 4000
0
1250
2500
-9.81
0.00
9.81
-1.0
0.0
1.0
2.0
-0.28
-0.14
0.00
0.14
eccentric phase concentric phase
Time (msec)
Vertical Force Fz
Center of Mass
Power
Center of Mass
Velocity
Center of Mass
Position
Center of Mass
Acceleration
NewtonWattsmeter/secmetermeter/sec2
1a 1b 2
Caserotti, Aagaard et al. Eur J Appl Physiol 2001, Scand J Med Sci Sports Exerc 2008

92. 0 1000 2000 3000 4000
0
2500
5000
-2500
0
2500
5000
-1.0
0.0
1.0
2.0
-0.28
-0.14
Time (msec)
Vertical
Force Fz
Power
Velocity
NewtonWattsmeter/sec
eccentric
peak power Pecc
concentric
peak power Pcon
Rate of Force
Development
RFD = ΔFz/Δt
eccentric
peak velocity Vecc
concentric
peak velocity Vcon
-1000
0
1000
2000
2500
-9.81
0.00
9.81
-1.0
0.0
1.0
2.0
-0.28
-0.14
0.00
0.14
eccentric phase concentric phase
Center of Mass
Power
Center of Mass
Velocity
Center of Mass
Position
Center of Mass
Acceleration
Wattsmeter/secmetermeter/sec2
1a 1b 2

93. Jakobsen, Aagaard et al, Human Movement Sci 2012
dynamic RFD measured from acc-dec transition point (peak Vdownward) to +50 ms
CMJ Power testing
Changes in dynamic RFD and CMJ performance
with resistance training
Pre and Post 12 wks heavy-resistance strength training (ST)

94. Jakobsen, Aagaard et al, Human Movement Sci 2012
Vertical ground reaction force Fz pre and post training
Rate of
Force Development
RFD = ΔFz/Δt
pre
post
CMJ Power testing
Changes in dynamic RFD and CMJ performance
with resistance training
Pre and Post 12 wks heavy-resistance strength training (ST)

95. Vertical ground reaction force Fz pre and post training
Rate of
Force Development
RFD = ΔFz/Δt
pre
post
CMJ Power testing
Changes in dynamic RFD and CMJ performance
with resistance training
Pre and Post 12 wks heavy-resistance strength training (ST)
Kinetic parameters
RFD +78%
Ppeak +10%
LL Stiffness +38%
Jump execution
Jump Height +17%
Tecc-phase -17%
Tcon-phase -11%
Jakobsen, Aagaard et al, Human Movement Sci 2012

96. Vertical ground reaction force Fz pre and post training
Rate of
Force Development
RFD = ΔFz/Δt
pre
post
CMJ Power testing
Changes in dynamic RFD and CMJ performance
with resistance training
Pre and Post 12 wks heavy-resistance strength training (ST)
Kinetic parameters
RFD +78%
Ppeak +10%
LL Stiffness +38%
Jump execution
Jump Height +17%
Tecc-phase -17%
Tcon-phase -11%
Jakobsen, Aagaard et al, Human Movement Sci 2012
STRONG NEUROMUSCULAR COMPONENT:
Strong positive correlations were observed between
pre-to-post gains in Hamstring rate-of-EMG rise
(RER) and increases in CMJ RFD (r = .83, p < 0.01)
and lower limb stiffness (r = .80, p < 0.01).

97. Jakobsen,
Aagaard et al,
Human
Movement
Sci 2012
Lateral Quadriceps (VL)
Medial Quadriceps (VM)
Center Quadriceps (RF)
Lateral Hamstrings (BF)
Medial Hamstrings (ST)
Lateral Gastroc (GL)
Medial Gastroc (GL)
Vertical ground
reaction
force (Fz)
CMJ and EMG testing Pre and Post 12 wks resistance training