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) Hookes 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: Tendon Muscle Fibre Muscle Muscle-tendon-unit (MTU) Joint Leg Methods of Calculating Lower Extremity Stiffness during Dynamic Movements Spring-Mass-Model (K vert ) Spring-Mass-Model (K leg ) K leg during Running Torsional-Spring-Model (K joint ) K knee during Running Example MTU & Hills Muscle Model Vastus Lateralis Gastrocnemius Hills Muscle Model Tendon Stiffness (K ten ) (Hopping) Tendon stiffness (Nmm-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 length, broken line = muscle length 57 Lower Extremity Stiffness Regulation during Dynamic Movements Joint Stiffness K ankle : 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) K knee : 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 exion the moment arm of the vertical GRF and thus K leg (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: K hip in females (Schmitz and Shultz, 2010) Plantar flexor: K ten (AT) in males & females (Muraoka et al., 2005) Knee extensor and plantar flexor: K ten (AT & PT) in males (Karamanidis et al., 2008) Eccentric strength: Knee flexors & extensors: K leg & K knee (DL only) during high intensity forward hopping (McMahon and Graham-Smith, 2010) Influence of Lower Extremity Stiffness on Functional Performance K leg 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) 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) K leg and Performance (Contd) Too Much K leg 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 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 K ten : Elastic energy storage (Butler et al., 2003; Turner and Jeffreys, 2011) K ten and Performance Affect of Static Stretching, Training and Coaching Cues on Lower Extremity Stiffness Static Stretching Acute: 10 min calf stretch - K ten & Hysteresis (Kubo et al., 2001a) 5 min calf stretch - K ten & Youngs Modulus (Burgess et al., 2009) - greater decreases in female subjects 5 min calf stretch - K ten & Hysteresis (Kubo et al., 2002b) Changes above due to Viscosity & Elasticity 3 min calf stretch - K leg 2.2Hz) (Hobara et al., 2011) Chronic: 5 x 45s (15s rest) calf stretch 2 x day for 3 weeks: K ten & Hysteresis (Kubo et al., 2002a) Isotonic Resistance Training 6 weeks of: Eccentric heel drops (BW): K ten (Mahieu et al., 2008) 8 weeks of: Calf raises (70% 1RM): K ten & Hysteresis (Kubo et al., 2002c) 12 weeks of: Leg extension (70% 1RM): K ten (Kongsgaard et al., 2007) 14 weeks of: Leg extension/leg press (80% 1RM): K ten (Reeves et al., 2003a,b) 6 months of: BW squat: K ten (Kubo et al., 2003) Isometric Resistance Training 12 weeks of isometric knee extension performed at 70% MVC for 15-20s: K ten (Kubo et al., 2001c,d; 2006; 2009) muscle size and RFD (Kubo et al., 2001d) K ten 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: K ten (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): K ten (Four et al., 2010a,b) Trained with high volume: 36 sessions in total consisting of jumps per session Comparing Training Methods 6 weeks of Plyometric (DJ) vs Isometric (Plantar): Plyo: K ten (29%), RFD (19%) & SJ height (59%) Iso: K ten (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: K ten, K ankle, SJ height Plyo: K ten, K ankle, 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: K leg during CMJ Isotonic + Plyo: K leg (Toumi et al., 2004) 10 weeks of Isotonic (75-90% 1RM back squats) vs Power (0-30% 1RM Jump Squats): Isotonic: K leg Power: K leg during 0% 1RM jump squat (Cormie et al., 2010) Comparing Training Methods Sprint versus endurance training: Sprinters had K leg 1.5/3.0 Hz & DJ 30cm) Sprinters had K knee 1.5 Hz) Sprinters had K ankle 3.0 Hz) Sprinters had contact time & flight time Sprinters had K ten (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 back squats/deadlifts) plus Plyometrics (CMJ/DJ): During CMJ: K leg During DJ 30, 60, 90cm: K leg (Hunter and Marshall, 2002) Endurance Training No effect of endurance training on mechanical properties (i.e. K ten /Youngs 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 K leg 2.2 Hz) than untrained subjects (Hobara et al., 2008b) Coaching Cues K leg 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: 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 K leg & K joint Training Summary For increases in K leg & K joint to occur, training should: 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 K ten 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?