MAXIMAL NEUROMUSCULAR PERFORMANCE
LECTURE NOTES
by
MYRIAM DE GRAAF
LECTURE 1
Regarding muscle output there are always muscle-tendon properties and muscle activation.
Therefore muscle physiologist always want to understand what is going on in the muscle whilst
controlling activation (electrical stimulation and/or isolated muscle models). Even during voluntary
effort researchers will check muscle activation, since it determines which MU’s are active and hence
how the muscle will function.
Constructing the Force-Velocity relationship of the muscle
Draw a force time profile of a single short (2s) maximal voluntary isometric contraction and an
electrically stimulated contraction (2s, 100 Hz) in the same figure.
How can we vary the force level in both situations?
Force levels at maximal voluntary isometric contraction can be varied by changing the joint
angle and thus the length of the sarcomeres (Length-force relationship). Force levels in an electrically
stimulated contraction can also be varied by changing the stimulation frequency.
What happens with the length of the muscle fibers and tendons during the different phases of
an isometric contraction.
At the start fiber length will decrease slightly as cross-bridges form and the myosin head
performs its powerstroke. This lengthens the tendons. The muscle itself does not change length
(which makes it an isometric contraction). During the rest of the contraction all lengths are constant.
How to design measurements to construct a force (power)-velocity relationship?
Measure force (preferably with set-frequency electrical stimulation) at varying velocities.
However there are multiple force-velocity relationships for different situation (muscle starting length,
muscle type, temperature, preceding contractions etc.).
LECTURE NOTES
by
MYRIAM DE GRAAF
LECTURE 1
Regarding muscle output there are always muscle-tendon properties and muscle activation.
Therefore muscle physiologist always want to understand what is going on in the muscle whilst
controlling activation (electrical stimulation and/or isolated muscle models). Even during voluntary
effort researchers will check muscle activation, since it determines which MU’s are active and hence
how the muscle will function.
Constructing the Force-Velocity relationship of the muscle
Draw a force time profile of a single short (2s) maximal voluntary isometric contraction and an
electrically stimulated contraction (2s, 100 Hz) in the same figure.
How can we vary the force level in both situations?
Force levels at maximal voluntary isometric contraction can be varied by changing the joint
angle and thus the length of the sarcomeres (Length-force relationship). Force levels in an electrically
stimulated contraction can also be varied by changing the stimulation frequency.
What happens with the length of the muscle fibers and tendons during the different phases of
an isometric contraction.
At the start fiber length will decrease slightly as cross-bridges form and the myosin head
performs its powerstroke. This lengthens the tendons. The muscle itself does not change length
(which makes it an isometric contraction). During the rest of the contraction all lengths are constant.
How to design measurements to construct a force (power)-velocity relationship?
Measure force (preferably with set-frequency electrical stimulation) at varying velocities.
However there are multiple force-velocity relationships for different situation (muscle starting length,
muscle type, temperature, preceding contractions etc.).
