Post-operative effects on insulin resistance and specific tension of single human skeletal muscle fibres

We have explored the extent to which the maximal velocity of unloaded shortening (V max ), the force generated per unit cross-sectional area (P 0 ) and the curvature of the forcevelocity relationship (a/P 0 in the Hill equation) contribute to differences in peak power of chemically skinned single fibres from the quadriceps muscle of healthy young male subjects. The analysis was restricted to type I and IIA fibres that contained a single type of myosin heavy chain on electrophoretic separation. Force-velocity relationships were determined from isotonic contractions of maximally activated fibres at 15• C. Mean (± s.d.) peak powers were 1.99 ± 0.72 watts per litre (W L −1 ) for type I fibres and 6.92 ± 2.41 W L −1 , for type IIA fibres. The most notable feature, however, was the very large, sevenfold, range of power outputs within a single fibre type. This wide range was a consequence of variations in each of the three components determining power: P 0 , V max and a/P 0 . Within a single fibre type, P 0 varied threefold, and V max and a/P 0 two-to threefold. There were no obvious relationships between P 0 and V max or between P 0 and a/P 0 . However, there was a suggestion of an inverse relationship between a/P 0 and V max , the effect being to reduce, somewhat, the impact of differences in V max on peak power. In searching for the causes of variation in peak power of fibres of the same type, it appears likely that there are two factors, one that affects P 0 and another that leads to variation in both V max and a/P 0 .

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Variation in the determinants of power of chemically skinned human muscle fibres

Gilliver

Degens

Rittweger

et al. 2009

“…The experimental procedure and composition of the different solutions have been described in detail elsewhere (Degens et al 1999; Gilliver et al 2009). Briefly, on the day of the experiments muscle bundles were incubated for 20 min in a relaxing solution containing 1% Triton X‐100 to ensure membrane permeabilization.…”

Section: Methodsmentioning

confidence: 99%

What causesin vivomuscle specific tension to increase following resistance training?

Erskine

Jones

Maffulli

et al. 2010

Self Cite

It is not known why in vivo muscle specific tension increases following resistance training in humans but changes in muscle fibre-type composition, increased single-fibre specific tension or lateral force transmission might provide explanations. Lateral force transmission would increase specific tension but decrease contraction velocity, thus not affecting maximal power per unit muscle volume. In vivo muscle specific tension, power output and muscle volume were determined in the quadriceps femoris of 42 young men, while myosin heavy chain (MyHC) isoform composition, single-fibre (SF) specific tension, SF maximal shortening velocity (V max ) and SF peak power (W max ) of the vastus lateralis were established in a subsample (n = 17) before and after high-intensity leg-extension resistance training (3 sessions week −1 for 9 weeks). Following training, in vivo muscle specific tension increased by 17% but the power output/muscle volume ratio remained unaltered. Furthermore, there was no relationship between the traininginduced decrease in MyHC IIX and the change in specific tension in vivo. In addition, SF specific tension, V max and W max were unchanged following training. In conclusion, a change in fibretype composition does not explain the increased in vivo specific tension, nor does it seem likely that increased myofilament packing occurred with resistance training. However, an unchanged in vivo power per unit muscle volume is in accordance with the notion of enhanced lateral force transmission after strength training.

“…Sarcomere length of the resting fibre was set at 2.6 μm at the start of the experiment and checked at regular intervals thereafter. Fibre diameter was measured at three places while suspended in the air, and cross‐sectional areas were calculated assuming the fibre to have a circular cross‐section (Degens et al 1999; Degens & Larsson, 2007). No correction was made for swelling of the fibres during skinning.…”

Section: Methodsmentioning

confidence: 99%

Effects of submaximal activation on the determinants of power of chemically skinned rat soleus fibres

Gilliver

Degens

Rittweger

et al. 2010

Reducing the activating calcium concentration with skinned fibres is known to decrease isometric force and maximal shortening velocity, both of which will reduce the peak power. However, power is also a function of the curvature of the force-velocity relationship, and there is limited information on how changes in activating calcium affect this important property of muscle fibres. Force-velocity relationships of permeabilized single type I fibres from rat soleus muscle were determined using isotonic contractions at 15• C with both maximal (pCa 4.5) and submaximal activation (pCa 5.6). The rate of tension redevelopment (k tr ), which provides a measure of sum of the apparent rate constants for cross-bridge attachment and detachment (f app + g app ) following a rapid release and restretch, was also measured. Compared with pCa 4.5, specific tension (P o ) at pCa 5.6 declined by 22 ± 8% (mean ± s.d.) and the maximal velocity of shortening (V max ) fell by 44 ± 7%, but curvature of the force-velocity relationship (a/P o ) rose by 47 ± 31%, indicating a less concave relationship. The value of k tr declined by 23 ± 7%. The change in a/P o reduced the impact of changes in P o and V max on peak power by approximately 25%. Fitting the data to Huxley's model of cross-bridge action suggests that lower activating calcium decreased both the rate constant for cross-bridge attachment (f ) and that for detachment of negatively strained cross-bridges (g 2 ). The fact that V max (and thus g 2 ) changed to a greater extent than k tr (f app + g app ) is the reason that reduced activation results in a reduction in curvature of the force-velocity relationship.