Biomechanics in strength training: selected applied topics

1. Sports Biomechanics in
Strength Training;
Selected Applied Topics
by Mahdi Cheraghi
26th Strength & Conditioning Coaching Course
National Olympic Academy of IRAN
Dec 22 2019-Jan 2 2020
1

2. • WHY IS SHORTENING VELOCITY LIMITED?
• Human muscle cannot dissociate myosin heavy chains from actin
filaments faster than what is performed by myosin ATPase.
• type II fibers’ cross-bridge dissociation occurring 4–9 times
faster than type I fibers
2

3. Force-velocity, force-power, velocity power, and
optimal load relationship
3

4. Power
4

5. 5

6. 6

7. WEIGHTLIFTING DERIVATIVE FORCE–VELOCITY CURVE
7

8. 8

9. 9

10. • Relative power outputs for various exercises. The relative power outputs noted will
vary depending upon the load lifted, the level of athletes, athletes level of
strength, and the technique used in the lift.
• *Loads of between 75 and 85% of 1repetition maximum produce the highest
power outputs; **loads of 0–30% produce the highest power outputs
10

11. Explosive strength or RFD
• Explosive muscle strength: Ability to produce high peak Rate of Force
Development (RFD)
• Can be produced both dynamically and isometrically
• contraction times of 50–250 milliseconds are often associated with fast
movements such as jumping, sprinting, or changing of direction and
• No enough time to produce maximal force in sport activities (at least300-500 ms)
11

12. 12

13. 13

14. Critical time periods; importance of RFD
14

15. RFD or Explosive strength
Methods to improve RFD:
• Weaker , young and untrained individual: heavy load resistance exercise
• Stronger more experienced athletes : light load ballistic exercise
• Ballistic exercises : are ‘‘preprogrammed’’ exercises produce as much force as possible in
short periods of time (i.e., ballistic movements), with the goal of projecting the accelerated
object into free space (e.g., jumping, throwing, kicking).
• when attempting to maximize the rate of force development and power output a mixed
training approach is recommended :(heavy strength training + Ballistic exercises)
15

16. Backward Running!
• Muscle Activation:
-leg extensor
-Hip flexor
range between 53.3 and 189.6%
• BR can be used to increase leg strength and power and restore
muscle balance
• average muscle force per unit ground force is substantially higher
(14%) for BR than FR
• average active muscle length being 4% shorter during BR than FR
so higher activation
• even at matched absolute speeds, this means that the muscle spent
4% more time in a concentrically contracted state
16

17. • The quadriceps and tibialis anterior primarily serve to attenuate eccentric braking
force during early foot–ground contact while the plantar flexors, hamstrings and
gluteal muscles assist in forward propulsion in FR.
• The functional roles of lower limb muscles are interchanged between BR and FR:
- the anterior muscles of the legs become the primary source of propulsion and
posterior muscles absorb braking forces during BR
• muscle firing patterns are unique to running direction
• utility of this knowledge provides a method for reducing eccentric strain on desired
musculotendinous structures of the leg, while potentially developing greater
concentric contractile adaptations
• patellofemoral joint compressive force (PFJCF), is on average 24% lower during BR
than FR
17

18. • Braking and Propulsive Forces:
- mean force experienced while braking is greater in FR, while the mean
force necessary for propulsion is greater during BR
- difference between BR and FR is due to a significant increase of the
average propulsive power with a non-significant change in average braking
power.
- therefore indicating that FR is more reliant on the elastic components of
the motor unit, while BR relies more heavily on the contractile
component.
18

19. • Rate of Force Development:
- Rate of force development during BR has been shown to be
approximately 22% greater than FR across speeds ranging from 1.75
to 3.5 m s-1
- BR is less reliant on the parallel and series elastic components of
muscle, and appears to require greater recruitment of the
contractile components, particularly at greater running speeds.
- greater demands are placed on alternative sensory systems to
maintain positional awareness
19

20. • aerobic capacity could be improved from BR training due to the relatively larger
acute energetic costs and cardiopulmonary demands BR places on the body
compared to FR
• BR training may be used to improve change of direction performance and maintain
linear forward sprint-running performance.
20

21. Movement pattern
21

22. 22

23. 23

24. 24

25. Sample Program
25

26. Sample Program; resisted
26

27. 27

28. 28

29. Velocity-Based Training
WHY SHOULD IT BE USED?
• First, VBT has distinct advantages over other autoregulatory methods
• Second, VBT can identify proper training loads
• Third, VBT helps identify optimal velocities and specific loads
• Fourth, VBT provides immediate feedback that can play a role in
motivation
29

30. • increases in life stress increased the incidence of injury 3-fold in some
athletes
• individual stressors (e.g., sports stress, life stress, and social stress) will
result in day-to-day fluctuations in the ability to move external resistances
• there is a high positive correlation between the mean velocity of the
barbell and %1RM.
• Although the 1RM may fluctuate over time, the %1RM and mean velocity
remain quite stable.
• 1RM estimated using the velocity load profile (±18%)
Goal 70% 1RM may in actuality be lifting in a range of 52%–88% of
1RM!!!!!!
30

31. SPECIFICITY OF TRAINING
• Back squat: 100% 1RM moving at a velocity of approximately 0.3 m/s.
• Bench press: 100% 1RM moving at a velocity of approximately 0.15 m/s
• Strength-speed: moving a moderately heavy load at a moderate velocity
( mean velocity of 0.75–1.0 m/s )
• Speed-strength: moving a lighter load at high velocity
(mean velocity of 1.0–1.5 m/s)
• Starting-strength: the ability to overcome inertia rapidly and is developed by using
extremely light loads moved at extremely high velocities, ex. to rapidly overcome
inertia on their first step to achieve high-velocity movements
(ranges from 1.3 to 1.8 m/s and higher)
• hang cleans: mean velocity of the bar was between 0.6 and 0.8 m/s, far below the
recommended 1.4 m/s velocity for this lift
31

32. 32

33. 33

34. 34

35. 35

36. • Ground forces during sprint running. Faster sprinters (black line) produce greater
forces in a shorter time (often <0.1s) than slower sprinters (grey line). The ability
to produce large forces rapidly against the ground is a key to successful sprinting.
• Sprinters has stiffer Achilles tendons than non-runners. This should allow them
to cope better with forces of over 900kg placed on the tendon and to recoil
faster
36

37. 37

38. Training for Stiffness
38

39. 39

40. • emphasis on the power catch position for the snatch/clean may provide
development of stiffness capabilities about the knee in weightlifting exercises and
their derivatives.
40

41. Human strength curve
41

42. Variable Resistance Training (VRT)
• sticking region is dependent on loading and
accounts for 35–45% of the range of
movement

43. Elastic Band: Resisted and Assisted?
• Resistance load to improve peak power during explosive movements when
elastic bands and free weights in the back squat:
- 20–35% resistance by elastic bands &
- 65–80% for free weight loaded

44. Elastic Band: Resistive
• decrease or remove momentum from a system
• progressively increased tension
• promote the progressive recruitment of higher-order motor units
• improvements in RFD have been shown after training with resistive elastic
band
• more appropriate modality for developing the force–velocity capabilities
• greater EMG activity in eccentric contractions during Jump squat
• resulting higher peak power

45. Assistive
• during an overspeed training phase
• more desirable during periods of heavy competition when athlete loads
may be compromised by higher levels of fatigue.
• increased shortening rate and
• neuromuscular system activation reported as potential underlying
mechanisms

46. Chains; Optimizing the Stimulus
• in the linear hanging method, only 35%-45% of the total chain weight is
added to the ascending strength curve; the rest of the chain simply hangs
as static weight
• using the double-looped method 80%-90% of the chain weight is
progressively added to the total system load
• nearly twofold difference in the amount of variable resistance!!!

48. Chains or Bands?
• Neither is better!
• Chains: challenges proprioceptive stability because of wobbling
• Bands: Little more stability because of anchors
• Both: intera-repetition PAP: surplus neural drive at the bottom of the
exercises resulting in explosive initiation of concentric
• Greater power output at the initiation of concentric portion

49. Chains or Bands?
• Elastic Bands: When force characteristics are accumulative toward the end
of a movement (punch in boxing, vertical jump in Basketball)
• Chains: when requireing a consistant application of force (scrummaging in
rugby, block start in sprinting)
49

50. “Thank you”
Mahdi Cheraghi
Sports Biomechanics center
Email: mahdicheraghi26@gmail.com
: @mahdicheraghi
Figure: Mid-thigh pull test using force platform to measure RFD and maximal strength; athlete: Hasan Taftian
(Olympian Sprinter) 50