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**Susanne Lipfert** · October 28, 2010, 07:38 PM

summary: vmax of human muscle

Friday, October 29, 2010, 11:22 AM

thank you biomch-lers!

here is the summary of relpies to my post regarding vmax and curvature
of human skeletal muscle.
I was wondering where the significant differences of values reported
in the literature come from.

first of all, and not surprisingly, it is very difficult to measure
muscle parameters from intact human muscle other than using cadavers
or ultrasound.
second, for data available in the literature, one has to note the
temperature at which measurements were taken and account for the
thermal dependence of contraction speed.
there are countless other points to note and account for, e.g. the
used fiber preparations, modified hill functions or compensation
errors in muscle models.

I found reading these two papers very revealing:

Bennett, A. F. (1984). Thermal dependence of muscle function. Am J
Physiol 247, R217-229.

Domire, Z. J. and Challis, J. H. (2010). A critical examination of the
maximum velocity of shortening used in simulation models of human
movement. Computer Methods in Biomechanics and Biomedical Engineering.

a selection of replies are attached below.

thanks again for your valuable help!
cheers
suzi :-)
____________________________
S u s a n n e L i p f e r t
Locomotion Lab
University of Jena, Germany
+49 (0) 3641-945-734/9 (desk/lab)
s.lipf@uni-jena.de
www.lauflabor.de

--------------------------- Henry Astley ------------------------------

As far as Vmax goes, the paper states the fibers are at 12C, far below
human operating temperature of 37C (probably to prevent them from
breaking down too rapidly). Using a ballpark estimate of 2 for Q10,
that means a fiber operating at 1.2 L/s at 12C would be shortening at
6.8 L/s at 37C. A higher Q10 would mean an even bigger increase with
temperature, with the appropriate caveat that Q10 tends to level off
near an organism's preferred operating temperature.

Henry Astley

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--------------------------- Daniel Hahn -------------------------------

I think you should be very carefully when trying to estimate maximum
power output of a human muscle, especially when activated voluntarily.
However, it is not clear what kind of data you have. You are talking
about muscle fibres, so is your data based on isolated muscle fibre
experiments or do you like to estimate power output for intact
muscle-tendon units in humans during naturally movements (where you
only can asses muscle fascicles by ultrasound but not fibres)?
To my knowledge, unfortunately there is no measurement of vmax of
muscle fascicles for an intact in vivo human muscle. Moreover you
should be aware that curvature of F-v curves changes depending several
factors like e.g. muscle length and activation level. Thus, in my
opinion Hills constant a can't be assumed to have a fix value (0.25).
Moreover, already 1964 Hill himself modified his hyperbolic function
by replacing constant a by the function a = 0.16F0 + 0.18F, with
F0=maximum force and F=force at a given velocity. (However, I do not
know why people usually do not use it, perhaps due to the simplicity
of the original Hill-function).

Cheers
Daniel

Hill AV. The Effect of Load on the Heat of Shortening of Muscle. Proc
R Soc Lond B Biol Sci 159: 297-318, 1964.

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--------------------------- Glen Lichtwark ----------------------------

Two very important things to note about Bottinelli's data -

1. These experiments are performed on skin fibre preparations, which
don't always scale particularly well to the whole muscle level
2. The experiments are performed at low temperatures - typically 10-15
degrees. The lower the temperature the slower the peak contraction
speed. You can estimate the Vmax from the known Q10 of approximately
2-2.5 (Bennett, 1984). If we assume a Vmax of 0.8 measured at 12 deg
we can work out the Vmax at 37 degrees.

Q10 = (R2/R1)^[10/(T2-T1)]

Rearranging - R2 = (Q10^(1/[10/(T2-T1)]))*R1

Substitute values - Q10 = 2.5, R1 = 0.8, T2 = 37, T1 = 12
R2 = 7.9 Lo/s

Vmax of 7.9 Lo/s. This goes down to 4.5 Lo/s if we use a Q10 = 2.

Q10 values are reported in Bottinelli's papers, however not for Vmax.
I also think the values reported a little high compared to intact
fibres.

I hope this helps,

Glen

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--------------------------- At Hof ------------------------------------

I have not read yet the Bottinelli paper, but I am afraid that their
results must be incorrect. I was involved with the work of Van
Zandwijk (1998, Biol Cybern 79:121-130) and still am convinced of the
valid results. They give a = 0.13 - 0.30 and b = a.vmax = 1.4-3.0 rad
/s = = 1.75 - 3.7 L/s for soleus. (This gives vmax around 12 L/s. )The
parameter b = n.vmax is the most important for modeling. To measure
maximum speed vmax, and thus n = b/vmax is very difficult for human
muscles in ergometers. These values are in agreement with most other
work that I know of, but you may be more familiar with recent work
than I am. The values of Bottinelli are indeed incredibly low. Vmax =
0.3 L/s and n = 0.03 would lead to a time constant for the isometric
force of some 30 seconds, instead of 0.3 s.
Success with your inquiry,

At Hof

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vmax of human muscle

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