Lower Extremity Stiffness
Advanced Strength & Conditioning
John McMahon BSc (Hons), ASCC, CSCS
Lecture Aims
• To introduce the mechanical concept of lower
extremity stiffness and methods of calculation
• To examine how lower extremity stiffness is
regulated during dynamic movements
• To discuss the influence of lower extremity
stiffness on functional performance
• To explain the affect of static stretching,
training and coaching cues on lower extremity
stiffness
What is Stiffness?
• Stiffness describes the relationship between a
given force and the deformation of an object
or body (Butler et al., 2003; Brughelli and
Cronin, 2008a)
• Hooke’s Law:
F = kx
rearranged to
k = ∆F
∆x
• The spring constant (k) describes the stiffness
of an ideal spring-mass-system
Compartments of Stiffness
• Lower extremity stiffness can be determined
at various levels within the leg:
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Tendon
Muscle Fibre
Muscle
Muscle-tendon-unit (MTU)
Joint
Leg
Methods of Calculating Lower
Extremity Stiffness during Dynamic
Movements
Spring-Mass-Model (Kvert)
Spring-Mass-Model (Kleg)
Kleg during Running
Torsional-Spring-Model (Kjoint)
Kknee during Running
Example MTU & Hill’s Muscle Model
Vastus Lateralis
Gastrocnemius
Hill’s Muscle Model
Tendon Stiffness (Kten) (Hopping)
Tendon stiffness (N·mm-1) is
determined from the slope
of the elongation – force
relationship
The same method is used
to calculate muscle fibre,
muscle and MTU stiffness
MTU Behavior (Hopping)
Separation of muscle and tendon components from the
whole MTU during hopping
Solid line = MTU length, dotted line = tendon
57
length, broken line = muscle length
Lower Extremity Stiffness Regulation
during Dynamic Movements
Joint Stiffness
Kankle: main determinant during high frequency
movements with short contact times (fast
hopping/jumping; maximal velocity sprinting)
(Farley et al., 1998; Farley and Morgenroth, 1999; Hobara et al., 2010; Hobara et al.,
2011)
Kknee: main determinant during longer contact
time movements (slow hopping; maximal height
jumping; jogging; acceleration phase of sprinting)
(Arampatzis et al., 1999; Kuitunen et al., 2002; Hobara et al., 2009; Hobara et al., 2011)
Touchdown Joint Angles
Greater joint flexion
↑ the moment arm
of the vertical GRF
and thus ↓ Kleg
(Greene and McMahon, 1979;
McMahon et al., 1987; Farley et al.,
1998; Hortobagyi and DeVita, 1999;
Moritz and Farley, 2004; Hobara et al.,
2010)
Muscle Recruitment
Magnitude of pre-/post-landing agonist muscle activation
and co-activation of antagonists:
• Co-activation during stair descent (elderly population only)
• For males: GM, GL & VL during DJ (20cm); VL & BF only
during DJ (40/60cm); GM, SOL (but not TA) during hopping
• For females: same as males during DJ (20cm), but GM and
VL only (not BF) during DJ 40cm (quad dominant strategy)
(Farley et al., 1998; Hortobagyi and DeVita, 2000; Arampatzis et al., 2001a; Arampatzis et al.,
2001b; Hobara et al., 2007; Hsu et al., 2007; Hobara et al., 2010)
Muscle Strength
Isometric strength:
Knee flexor: Khip in females (Schmitz and Shultz, 2010)
Plantar flexor: Kten (AT) in males & females (Muraoka et
al., 2005)
Knee extensor and plantar flexor: Kten (AT & PT) in
males (Karamanidis et al., 2008)
Eccentric strength:
Knee flexors & extensors: Kleg & Kknee (DL only)
during high intensity forward hopping (McMahon and
Graham-Smith, 2010)
Influence of Lower Extremity
Stiffness on Functional Performance
Kleg and Performance
• ↓ ground contact times (Farley et al., 1991; Arampatzis et al.,
2001)
• ↑ hopping frequency (Farley et al.,1991; Granata et al.,2001)
• ↑ stride frequency (McMahon et al., 1987; Farley and Gonzalez,
1996)
• ↓ stride length (McMahon and Cheng, 1990; Derrick et al., 2000;
Kerdock et al., 2002)
Kleg and Performance (Cont’d)
• ↑ maximal velocity running (Farley and Gonzalez, 1996;
Stefanyshyn and Nigg, 1998; Arampatzis et al., 1999; Seyfarth et al., 2002)
• ↑ running economy (McMahon and Cheng, 1990; Heise and
Martin, 1998; Dutto and Smith, 2002; Kerdock et al., 2002)
• ↑ vertical jump height (from low drop
heights) (Arampatzis et al., 2001)
• ↑ horizontal hop distance (McMahon and Graham-Smith,
2010)
Too Much Kleg…
↓ vertical jump height (Walshe and Wilson,
1997; Arampatzis et al., 2001; Laffaye et al., 2005)
↓ horizontal jump distances (Seyfarth et al.,
1999; 2000)
↑ bony
injury risk
(Hewett et al.,
1996; Butler et
al., 2003)
The magnitude
of Kleg
requirements
depends upon
the task type
Kten and Performance
• ↑ RFD
• ↑ SJ height
• ↓ Tendon strain (injuries)
(Kubo et al., 2001d; Butler et al., 2003; Burgess et al., 2007; Kubo et al., 2007)
However, too much Kten:
• ↓ Elastic energy storage
(Butler et al., 2003; Turner and Jeffreys, 2011)
Affect of Static Stretching, Training
and Coaching Cues on Lower
Extremity Stiffness
Static Stretching
Acute:
• 10 min calf stretch - ↓ Kten & Hysteresis (Kubo et al., 2001a)
• 5 min calf stretch - ↓ Kten & Young’s Modulus (Burgess et al.,
2009)
- greater decreases in female subjects
• 5 min calf stretch - ↓ Kten & Hysteresis (Kubo et al., 2002b)
Changes above due to ↓ Viscosity & ↑ Elasticity
• 3 min calf stretch - ↔ Kleg (hopping @ 2.2Hz) (Hobara et al.,
2011)
Chronic:
• 5 x 45s (15s rest) calf stretch 2 x day for 3 weeks:
↔ Kten & ↓ Hysteresis (Kubo et al., 2002a)
Isotonic Resistance Training
6 weeks of:
• ‘Eccentric’ heel drops (BW): ↔ Kten (Mahieu et al., 2008)
8 weeks of:
• Calf raises (70% 1RM):↑ Kten & ↔ Hysteresis (Kubo et al.,
2002c)
12 weeks of:
• Leg extension (70% 1RM): ↑ Kten (Kongsgaard et al., 2007)
14 weeks of:
• Leg extension/leg press (80% 1RM): ↑ Kten (Reeves et al.,
2003a,b)
6 months of:
• BW squat: ↔ Kten (Kubo et al., 2003)
Isometric Resistance Training
12 weeks of isometric knee extension performed at
70% MVC for 15-20s:
• ↑ Kten (Kubo et al., 2001c,d; 2006; 2009)
• ↑ muscle size and RFD (Kubo et al., 2001d)
↔ Kten during above exercise when:
- Performed for short duration (1s)
- Performed at short muscle length (50 deg)
- Performed for < 8 weeks
Isometric Resistance Training
14 weeks of isometric plantar flexion performed
at 90% MVC for 3s:
• ↑ Kten (Arampatzis et al., 2007; 2010)
Authors concluded that the strain magnitude
during isometric training should exceed the
value experienced during habitual loading for
mechanical adaptations in tendon to occur.
Plyometric Training
14 weeks of plyometric training (SJ, CMJ, DJ
(35/40+50/60+65/80cm), hop over 40cm barrier):
• ↑ Kten (Fouré et al., 2010a,b)
Trained with high volume: 36 sessions in total
consisting of 200-600 jumps per session
Comparing Training Methods
6 weeks of Plyometric (DJ) vs Isometric (Plantar):
• Plyo: ↑ Kten (29%), ↑ RFD (19%) & ↑ SJ height (59%)
• Iso: ↑ Kten (62%), ↑ RFD (17%) & ↑ SJ height (64%)
(Burgess et al., 2007)
12 weeks of Isotonic (80% 1RM calf raise) vs Plyo (sledge
hopping & DJ 20 cm):
• Isotonic: ↑ Kten, ↔ Kankle,↑ SJ height
• Plyo: ↔ Kten, ↑ Kankle, ↑ SJ, CMJ & DJ height
(Kubo et al., 2007)
Comparing Training Methods
6 weeks of isotonic (70% 1RM leg press) vs isotonic +
Plyo (Barrier hops):
• Isotonic: ↔ Kleg
during CMJ
• Isotonic + Plyo: ↑ Kleg
(Toumi et al., 2004)
10 weeks of Isotonic (75-90% 1RM back squats) vs
Power (0-30% 1RM Jump Squats):
• Isotonic: ↑ Kleg
• Power: ↑ Kleg
during 0% 1RM jump squat
(Cormie et al., 2010)
Comparing Training Methods
Sprint versus endurance training:
• Sprinters had ↑ Kleg (hopping @ 1.5/3.0 Hz & DJ 30cm)
• Sprinters had ↑ Kknee (hopping @ 1.5 Hz)
• Sprinters had ↑ Kankle (hopping @ 3.0 Hz)
• Sprinters had ↓ contact time & ↑ flight time
• Sprinters had ↑ Kten (AT) & Plantar flexor Moments
(Harrision et al., 2004; Arampatzis et al., 2007; Hobara et al., 2008)
Combination Training
10 weeks of isotonic (90-100% RPE
squats/deadlifts) plus Plyometrics (CMJ/DJ):
• During CMJ: ↑ Kleg
• During DJ 30, 60, 90cm: ↓ Kleg
(Hunter and Marshall, 2002)
back
Endurance Training
• No effect of endurance training on mechanical
properties (i.e. Kten/Young’s Modulus) of the PT or
AT
(Rosager et al., 2002; Hansen et al., 2003; Karamanidis and Arampatzis, 2006; Arampatzis
et al., 2007)
• Endurance runners had ↑ Kleg (hopping @ 2.2 Hz)
than untrained subjects
(Hobara et al., 2008b)
Coaching Cues
Kleg can be manipulated by asking athletes to:
• “Reduce ground contact time”
• “Minimise knee flexion”
• “Jump as high as you can”
• “Jump high a little faster than your previous jump”
(Arampatzis et al., 2001b)
Tendon Training Summary
For increases in tendon stiffness to occur, training
should:
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Include high loads (>70% 1RM)
Involve high tendon strains (↑ drop heights)
If isometric, be performed at long muscle lengths
If isometric, be performed for at least 3s/rep
Be performed consistently for at least 6-8 weeks
Kleg & Kjoint Training Summary
For increases in Kleg & Kjoint to occur, training should:
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Include high loads (>75% 1RM)
Involve large muscle mass (Squats/Deadlifts)
Include both strength and power exercises
Be task specific
Be performed when technically competent
Be monitored to avoid excessive recruitment
Training Proposal
• Strength training and low-intensity plyometrics
(coached correctly) should proceed high-intensity
plyometric performance (for at least 6-8 weeks) in
order develop necessary Kten to help avoid
excessive tendon strains that may lead to injury.
• Plyometric training drills should be specific to the
lower extremity stiffness characteristics of each
athletes’ sport in order to enhance their
transferability to performance.
Any Questions?