Biomechanical Equations

1
Biomechanical Equations

• Work W FD
• Velocity V D/t
• Power P W/t
• Acceleration V/t

2
Biomechanical Factors in Human Strength

• Neural Control
• Recruitment the number of motor units involved
  in a muscle contraction
• Rate Coding the rate at which the motor units
  are fired (twitched)
• Much of the improvement in strength evidenced in
  the first few weeks of resistance training is due
  to neural adaptations
• Neural-based improvements will slow as the motor
  units become more efficient further gains in
  strength then need to be addressed through other
  measures
• Muscle Cross Sectional Area
• All else being equal, the F a muscle can generate
  is related to its cross-sectional area rather
  than the muscles volume
• Taller athletes may have longer muscles, and
  therefore more muscle volume however this muscle
  volume can be matched by an athlete with less
  muscle volume but more cross sectional area
• Elite gymnasts have large muscles when evaluated
  cross sectionally, and elite gymasts are
  typically not tall

3
Biomechanical Factors in Human Strength (cont.)

• Arrangement of Muscle Fibers
• Angle of Pennation a angle between the muscle
  fibers and an imaginary line between the muscles
  origin and insertion
• Pennate Muscle featherlike arrangement of
  muscle fibers enhances F capability for muscle
• contraction at high speed
• not optimal for eccentric,
• isometric or low-speed concentric
• F production
• Muscle Length
• A muscle at its resting length has more F
  generating capacity as the Actin and Myosin are
  at the most advantageous position for cross
  bridging

4
Biomechanical Factors in Human Strength (cont.)

• Joint Angle
• As the angle of a joint changes through its ROM,
  so too does the angle of insertion of the agonist
  muscle different joint positions result in a
  more advantageous use of the total muscle force
  (MF)
• Two joint muscles (i.e. hamstrings) are affected
  by the joint position of the two joints crossed
  by the muscle (i.e. hip and knee). For example,
  more F can be produced by the hamstrings during a
  leg curl when the hip is placed in flexion.
  Likewise, more F can be produced by the
  gastrocnemius for a prone leg curl when the ankle
  is dorsiflexed (toes and foot pulled upward).

5
Biomechanical Factors in Human Strength (cont.)

• Muscle Contraction Velocity
• As the velocity of a contraction increases, the F
  generating capabilities of the muscle decreases.
  This is demonstrated by the Force Velocity Curve.
  Conversely, as the velocity of a contraction
  slows, F generating capabilities increase
• From this F-V curve, it is evident that the
  greatest force production capability is with slow
  eccentric activities (i.e. eccentric component of
  a squat)
• Activities requiring high velocity concentric
  actions produce the lowest force (i.e. throwing a
  wiffle ball)

6
Biomechanical Factors in Human Strength (cont.)

• Strength-to-Mass Ration
• The ratio of the strength of the muscles involved
  in a movement to the mass of the body parts being
  accelerated is critical
• Increasing the strength of a muscle increases the
  F generating capacity, however, if there is an
  increase in total mass of the muscle, the ability
  to accelerate the body part may be limited
• In many sports there are optimal
  strength-to-mass, or power-to-weight ratios (i.e.
  sprinting, cycling, wrestling)
• Body Size
• Smaller athletes are stronger pound for pound
• As body size increases, body mass increases more
  rapidly than does muscular strength

7
References

• Baechle, TR. Earle, RW. Essentials of Strength
  Training and Conditioning, 2nd Ed. 2000. Human
  Kinetics.