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Dear all,
A number of interesting problems is addressed here. It may be good to
separate them carefully.
1) In my opinion the most interesting point is the question of
maximum activation. Paul Devita rightly points to this effect:
maximum moments in jumping or running are substantially higher than
those on an isokinetic dynamometer, and even more so, I might add,
than the so-called Maximum Voluntary Contraction. I am not so
informed on quadriceps, but in triceps surae (ankle plantarflexors)
typical peak values are, from a paper of ours in the press:
175 Nm isometric MVC
110 Nm in a TWO legged squat jump (one-legged seems to be higher)
155 Nm in landing after a 2-legged jump
225 Nm in sprinting
The point is even worse when it is considered that the muscle is not
isometric, but shortening at the time of peak moment. By reckoning
the effects of series-elasticity, we could estimate (rather roughly)
the peak 'active state' of the triceps surae, and got:
175 Nm isometric MVC (the same of course)
270 Nm in a TWO legged squat jump
150 Nm in landing after a 2-legged jump (eccentric contraction, thus
not so much higher)
500 Nm in sprinting!
In the EMGs the effect is also clearly visible: peak rectified EMG in
running can be 200% of 'MVC' or more (like Jacobs and Van Ingen
Schenau, 1992).
On this point I agree with Ton vd Bogerts remarks sub 3). In the
big leg muscles, there must be motor units (and probably the
strongest ones) which become only active in very brief actions at the
highest levels of activation. In small muscles e.g. in the hand, some
95% of maximum may be reached. McComas in his book "Skeletal Muscle"
(Human kinetics, 1996) on p. 211 discusses the problem, but in my
opinon he underestimates the effect.
Electrical stimulation is not the solution. In the big leg muscles is
is very difficult, painful and even dangerous to try maximal
stimulation. In the subject referred to above (a very tough guy) we
could reach 170 Nm, the others did not let us go above 120 Nm. (In
Scandinavia they might reach higher levels. ) I heard a story from a
well-known investigator who stimulated the knee extensors of a
colleage to such an extent, that the patella luxated with a loud
crack.
2) The inverse dynamics is quite prone to methodological errors,
Bogert point 1), but I do not suppose that it is very relevant here.
Agree with Vasilios Baltzopoulos.
3) Paul Devita gives a muscle force of 700 Nm. This is incorrect, see
remarks of Vasilios. You have probably used the moment arm of the
ergometer force transducer (some 20 cm) instead of that of the
patellar tendon, 4 cm.
4) Due to the effects of the series-elastic component, isokinetic
speed is only equal to shortening speed of the muscle fibres at the
peak of the moment (when dM/dt = 0). I have investigated this
problem, and the differences are very substantial. So only a single
point can be used to construct a force-velocity curve!
There are some interesting effects here, which surely warrant
further discussion and investigation.
Yours,
At Hof
Department of Medical Physiology &
Laboratory of Human Movement Analysis AZG
University of Groningen
Bloemsingel 10
NL-9712 KZ GRONINGEN
THE NETHERLANDS
Tel: (31) 50 3632645
Fax: (31) 50 3632751
e-mail: a.l.hof@med.rug.nl
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A number of interesting problems is addressed here. It may be good to
separate them carefully.
1) In my opinion the most interesting point is the question of
maximum activation. Paul Devita rightly points to this effect:
maximum moments in jumping or running are substantially higher than
those on an isokinetic dynamometer, and even more so, I might add,
than the so-called Maximum Voluntary Contraction. I am not so
informed on quadriceps, but in triceps surae (ankle plantarflexors)
typical peak values are, from a paper of ours in the press:
175 Nm isometric MVC
110 Nm in a TWO legged squat jump (one-legged seems to be higher)
155 Nm in landing after a 2-legged jump
225 Nm in sprinting
The point is even worse when it is considered that the muscle is not
isometric, but shortening at the time of peak moment. By reckoning
the effects of series-elasticity, we could estimate (rather roughly)
the peak 'active state' of the triceps surae, and got:
175 Nm isometric MVC (the same of course)
270 Nm in a TWO legged squat jump
150 Nm in landing after a 2-legged jump (eccentric contraction, thus
not so much higher)
500 Nm in sprinting!
In the EMGs the effect is also clearly visible: peak rectified EMG in
running can be 200% of 'MVC' or more (like Jacobs and Van Ingen
Schenau, 1992).
On this point I agree with Ton vd Bogerts remarks sub 3). In the
big leg muscles, there must be motor units (and probably the
strongest ones) which become only active in very brief actions at the
highest levels of activation. In small muscles e.g. in the hand, some
95% of maximum may be reached. McComas in his book "Skeletal Muscle"
(Human kinetics, 1996) on p. 211 discusses the problem, but in my
opinon he underestimates the effect.
Electrical stimulation is not the solution. In the big leg muscles is
is very difficult, painful and even dangerous to try maximal
stimulation. In the subject referred to above (a very tough guy) we
could reach 170 Nm, the others did not let us go above 120 Nm. (In
Scandinavia they might reach higher levels. ) I heard a story from a
well-known investigator who stimulated the knee extensors of a
colleage to such an extent, that the patella luxated with a loud
crack.
2) The inverse dynamics is quite prone to methodological errors,
Bogert point 1), but I do not suppose that it is very relevant here.
Agree with Vasilios Baltzopoulos.
3) Paul Devita gives a muscle force of 700 Nm. This is incorrect, see
remarks of Vasilios. You have probably used the moment arm of the
ergometer force transducer (some 20 cm) instead of that of the
patellar tendon, 4 cm.
4) Due to the effects of the series-elastic component, isokinetic
speed is only equal to shortening speed of the muscle fibres at the
peak of the moment (when dM/dt = 0). I have investigated this
problem, and the differences are very substantial. So only a single
point can be used to construct a force-velocity curve!
There are some interesting effects here, which surely warrant
further discussion and investigation.
Yours,
At Hof
Department of Medical Physiology &
Laboratory of Human Movement Analysis AZG
University of Groningen
Bloemsingel 10
NL-9712 KZ GRONINGEN
THE NETHERLANDS
Tel: (31) 50 3632645
Fax: (31) 50 3632751
e-mail: a.l.hof@med.rug.nl
---------------------------------------------------------------
To unsubscribe send SIGNOFF BIOMCH-L to LISTSERV@nic.surfnet.nl
For information and archives: http://isb.ri.ccf.org/biomch-l
---------------------------------------------------------------