scholarly journals Force-velocity-power and force-pCa relationships of human soleus fibers after 17 days of bed rest

1998 ◽  
Vol 85 (5) ◽  
pp. 1949-1956 ◽  
Author(s):  
J. J. Widrick ◽  
K. M. Norenberg ◽  
J. G. Romatowski ◽  
C. A. Blaser ◽  
M. Karhanek ◽  
...  
Keyword(s):  
Peak Power ◽  
Weight Bearing ◽  
Bed Rest ◽  
Force Transducer ◽  
Hindlimb Suspension ◽  
Peak Power Output ◽  
Type I ◽  
Shortening Velocity ◽  
Adult Men ◽  
Force Velocity

Soleus muscle fibers from the rat display a reduction in peak power and Ca2+ sensitivity after hindlimb suspension. To examine human responses to non-weight bearing, we obtained soleus biopsies from eight adult men before and immediately after 17 days of bed rest (BR). Single chemically skinned fibers were mounted between a force transducer and a servo-controlled position motor and activated with maximal (isotonic properties) and/or submaximal (Ca2+ sensitivity) levels of free Ca2+. Gel electrophoresis indicated that all pre- and post-BR fibers expressed type I myosin heavy chain. Post-BR fibers obtained from one subject displayed increases in peak power and Ca2+ sensitivity. In contrast, post-BR fibers obtained from the seven remaining subjects showed an average 11% reduction in peak power ( P < 0.05), with each individual displaying a 7–27% reduction in this variable. Post-BR fibers from these subjects were smaller in diameter and produced 21% less force at the shortening velocity associated with peak power. However, the shortening velocity at peak power output was elevated 13% in the post-BR fibers, which partially compensated for their lower force. Post-BR fibers from these same seven subjects also displayed a reduced sensitivity to free Ca2+( P < 0.05). These results indicate that the reduced functional capacity of human lower limb extensor muscles after BR may be in part caused by alterations in the cross-bridge mechanisms of contraction.

scholarly journals Effect of intermittent weight bearing on soleus fiber force-velocity-power and force-pCa relationships

1997 ◽  
Vol 82 (6) ◽  
pp. 1905-1910 ◽  
Author(s):  
J. J. Bangart ◽  
J. J. Widrick ◽  
R. H. Fitts
Keyword(s):  
Power Output ◽  
Peak Power ◽  
Weight Bearing ◽  
Peak Power Output ◽  
Type I ◽  
Shortening Velocity ◽  
Functional Changes ◽  
Maximal Activation ◽  
Force Velocity ◽  
Type I Fibers

Bangart, J. J., J. J. Widrick, and R. H. Fitts. Effect of intermittent weight bearing on soleus fiber force-velocity-power and force-pCa relationships. J. Appl. Physiol. 82(6): 1905–1910, 1997.—Rat permeabilized type I soleus fibers displayed a 33% reduction in peak power output and a 36% increase in the free Ca2+ concentration required for one-half maximal activation after 14 days of hindlimb non-weight bearing (NWB). We examined the effectiveness of intermittent weight bearing (IWB; consisting of four 10-min periods of weight bearing/day) as a countermeasure to these functional changes. At peak power output, type I fibers from NWB animals produced 54% less force and shortened at a 56% greater velocity than did type I fibers from control weight-bearing animals while type I fibers from the IWB rats produced 26% more absolute force than did fibers from the NWB group and shortened at a velocity that was only 80% of the NWB group mean. As a result, no difference was observed in the average peak power of fibers from the IWB and NWB animals. Hill plot analysis of force-pCa relationships indicated that fibers from the IWB group required similar levels of free Ca2+ to reach half-maximal activation in comparison to fibers from the weight-bearing group. However, at forces <50% of peak force, the force-pCa curve for fibers from the IWB animals clearly fell between the relationships observed for the other two groups. In summary, IWB treatments 1) attenuated the NWB-induced reduction in fiber Ca2+sensitivity but 2) failed to prevent the decline in peak power that occurs during NWB because of opposing effects on fiber force (an increase vs. NWB) and shortening velocity (a decrease vs. NWB).

Force-velocity and force-power properties of single muscle fibers from elite master runners and sedentary men

1996 ◽  
Vol 271 (2) ◽  
pp. C676-C683 ◽  
Author(s):  
J. J. Widrick ◽  
S. W. Trappe ◽  
D. L. Costill ◽  
R. H. Fitts
Keyword(s):  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Power Output ◽  
Peak Power ◽  
Isometric Force ◽  
Peak Force ◽  
Peak Power Output ◽  
Type I ◽  
Shortening Velocity ◽  
Force Velocity

Gastrocnemius muscle fiber bundles were obtained by needle biopsy from five middle-aged sedentary men (SED group) and six age-matched endurance-trained master runners (RUN group). A single chemically permeabilized fiber segment was mounted between a force transducer and a position motor, subjected to a series of isotonic contractions at maximal Ca2+ activation (15 degrees C), and subsequently run on a 5% polyacrylamide gel to determine myosin heavy chain composition. The Hill equation was fit to the data obtained for each individual fiber (r2 > or = 0.98). For the SED group, fiber force-velocity parameters varied (P < 0.05) with fiber myosin heavy chain expression as follows: peak force, no differences: peak tension (force/fiber cross-sectional area), type IIx > type IIa > type I; maximal shortening velocity (Vmax, defined as y-intercept of force-velocity relationship), type IIx = type IIa > type I; a/Pzero (where a is a constant with dimensions of force and Pzero is peak isometric force), type IIx > type IIa > type I. Consequently, type IIx fibers produced twice as much peak power as type IIa fibers, whereas type IIa fibers produced about five times more peak power than type I fibers. RUN type I and IIa fibers were smaller in diameter and produced less peak force than SED type I and IIa fibers. The absolute peak power output of RUN type I and IIa fibers was 13 and 27% less, respectively, than peak power of similarly typed SED fibers. However, type I and IIa Vmax and a/Pzero were not different between the SED and RUN groups, and RUN type I and IIa power deficits disappeared after power was normalized for differences in fiber diameter. Thus the reduced absolute peak power output of the type I and IIa fibers from the master runners was a result of the smaller diameter of these fibers and a corresponding reduction in their peak isometric force production. This impairment in absolute peak power production at the single fiber level may be in part responsible for the reduced in vivo power output previously observed for endurance-trained athletes.

scholarly journals Force-velocity and power characteristics of rat soleus muscle fibers after hindlimb suspension

1994 ◽  
Vol 77 (4) ◽  
pp. 1609-1616 ◽  
Author(s):  
K. S. McDonald ◽  
C. A. Blaser ◽  
R. H. Fitts
Keyword(s):  
Isometric Force ◽  
Fiber Type ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Hindlimb Suspension ◽  
Type I ◽  
Shortening Velocity ◽  
Power Characteristics ◽  
Sds Page ◽  
Force Velocity

The effects of 1, 2, and 3 wk of hindlimb suspension (HS) on force-velocity and power characteristics of single rat soleus fibers were determined. After 1, 2, or 3 wk of HS, small fiber bundles were isolated, placed in skinning solution, and stored at -20 degrees C until studied. Single fibers were isolated and placed between a motor arm and force transducer, functional properties were studied, and fiber protein content was subsequently analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Additional fibers were isolated from soleus of control and after 1 and 3 wk of HS, and fiber type distribution and myosin light chain stoichiometry were determined from SDS-PAGE analysis. After 1 wk of HS, percent type I fibers declined from 82 to 74%, whereas hybrid fibers increased from 10 to 18%. Percent fast type II fibers increased from 8% in control and 1 wk of HS to 26% by 3 wk of HS. Most fibers showed an increased unloaded maximal shortening velocity (Vo), but myosin heavy chain remained entirely slow type I. The mechanism for increased Vo is unknown. There was a progressive decrease in fiber diameter (14, 30, and 38%) and peak force (38, 56, and 63%) after 1, 2, and 3 wk of HS, respectively. One week of HS resulted in a shift of the force-velocity curve, and between 2 and 3 wk of HS the curve shifted further such that Vo was higher than control at all relative loads < 45% peak isometric force. Peak absolute power output of soleus fibers progressively decreased through 2 wk of HS but showed no further change at 3 wk.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of hindlimb suspension on the functional properties of slow and fast soleus fibers from three strains of mice

2003 ◽  
Vol 95 (6) ◽  
pp. 2425-2433 ◽  
Author(s):  
Julian E. Stelzer ◽  
Jeffrey J. Widrick
Keyword(s):  
Weight Bearing ◽  
Hindlimb Suspension ◽  
Type I ◽  
Shortening Velocity ◽  
Cross Sectional ◽  
Fast Fiber ◽  
Animal Strain ◽  
Slow Twitch ◽  
Fiber Atrophy ◽  
Fast Twitch

Cross-sectional area (CSA), peak Ca2+-activated force (Po), fiber specific force (Po/CSA), and unloaded shortening velocity ( Vo) were measured in slow-twitch [containing type I myosin heavy chain (MHC)] and fast-twitch (containing type II MHC) chemically skinned soleus muscle fiber segments obtained from three strains of weight-bearing and 7-day hindlimb-suspended (HS) mice. HS reduced soleus slow MHC content (from ∼50 to ∼33%) in CBA/J and ICR strains without affecting slow MHC content in C57BL/6 mice (∼20% of total MHC). Two-way ANOVA revealed HS-induced reductions in CSA, Po, and Po/CSA of slow and fast fibers from all strains. Fiber Vo was elevated post-HS, but not consistently across strains. No MHC × HS treatment interactions were observed for any variable for C57BL/6 and CBA/J mice, and the two significant interactions found for the ICR strain (CSA, Po) appeared related to inherent pre-HS differences in slow vs. fast fiber CSA. In the mouse HS models studied here, fiber atrophy and contractile dysfunction were partially dependent on animal strain and generally independent of fiber MHC isoform content.

Unilateral lower limb suspension does not mimic bed rest or spaceflight effects on human muscle fiber function

2002 ◽  
Vol 93 (1) ◽  
pp. 354-360 ◽  
Author(s):  
J. J. Widrick ◽  
S. W. Trappe ◽  
J. G. Romatowski ◽  
D. A. Riley ◽  
D. L. Costill ◽  
...  
Keyword(s):  
Lower Limb ◽  
Peak Power ◽  
Cell Damage ◽  
Bed Rest ◽  
Lower Leg ◽  
Human Muscle ◽  
Type I ◽  
Shortening Velocity ◽  
Skinned Muscle ◽  
Skinned Muscle Fibers

We used Ca2+-activated skinned muscle fibers to test the hypothesis that unilateral lower leg suspension (ULLS) alters cross-bridge mechanisms of muscle contraction. Soleus and gastrocnemius biopsies were obtained from eight subjects before ULLS, immediately after 12 days of ULLS (post-0 h), and after 6 h of reambulation (post-6 h). Post-0 h soleus fibers expressing type I myosin heavy chain (MHC) showed significant reductions in diameter, absolute and specific peak Ca2+-activated force, unloaded shortening velocity, and absolute and normalized peak power. Fibers obtained from the gastrocnemius were less affected by ULLS, particularly fibers expressing fast MHC isoforms. Post-6 h soleus fibers produced less absolute and specific peak force than did post-0 h fibers, suggesting that reambulation after ULLS induced cell damage. Like bed rest and spaceflight, ULLS primarily affects soleus over gastrocnemius fibers. However, in contrast to these other models, slow soleus fibers obtained after ULLS showed a decrease in unloaded shortening velocity and a greater reduction in specific force.

scholarly journals Altered single cell force-velocity and power properties in exercise-trained rat myocardium

2003 ◽  
Vol 94 (5) ◽  
pp. 1941-1948 ◽  
Author(s):  
Gary M. Diffee ◽  
Eunhee Chung
Keyword(s):  
Exercise Training ◽  
Power Output ◽  
Peak Power ◽  
Muscle Length ◽  
Work Capacity ◽  
Peak Power Output ◽  
Sprague Dawley ◽  
Shortening Velocity ◽  
External Work ◽  
Force Velocity

Myocardial function is enhanced by endurance exercise training, but the cellular mechanisms underlying this improved function remain unclear. The ability of the myocardium to perform external work is a critical aspect of ventricular function, but previous studies of myocardial adaptation to exercise training have been limited to measurements of isometric tension or unloaded shortening velocity, conditions in which work output is zero. We measured force-velocity properties in single permeabilized myocyte preparations to determine the effect of exercise training on loaded shortening and power output. Female Sprague-Dawley rats were divided into sedentary control (C) and exercise trained (T) groups. T rats underwent 11 wk of progressive treadmill exercise. Myocytes were isolated from T and C hearts, chemically skinned, and attached to a force transducer. Shortening velocity was determined during loaded contractions at 15°C by using a force-clamp technique. Power output was calculated by multiplying force times velocity values. We found that unloaded shortening velocity was not significantly different in T vs. C myocytes (T = 1.43 muscle lengths/s, n = 46 myocytes; C = 1.12 muscle lengths/s, n = 43 myocytes). Training increased the velocity of loaded shortening and increased peak power output (peak power = 0.16 P/Po × muscle length/s for T myocytes; peak power = 0.10 P/Po× muscle length/s for C myocytes, where P/Po is relative tension). We found no effect of training on myosin heavy chain isoform content. These results suggest that training alters power output properties of single cardiac myocytes and that this adaptation may improve the work capacity of the myocardium.

scholarly journals Peak force and maximal shortening velocity of soleus fibers after non-weight-bearing and resistance exercise

1997 ◽  
Vol 82 (1) ◽  
pp. 189-195 ◽  
Author(s):  
Jeffrey J. Widrick ◽  
Robert H. Fitts
Keyword(s):  
Resistance Exercise ◽  
Elevated Level ◽  
Fiber Diameter ◽  
Weight Bearing ◽  
Normal Weight ◽  
Peak Force ◽  
Type I ◽  
Shortening Velocity ◽  
Adult Rats ◽  
Cross Sectional

Widrick, Jeffrey J., and Robert H. Fitts. Peak force and maximal shortening velocity of soleus fibers after non-weight-bearing and resistance exercise. J. Appl. Physiol. 82(1): 189–195, 1997.—This study examined the effectiveness of resistance exercise as a countermeasure to non-weight-bearing-induced alterations in the absolute peak force, normalized peak force (force/fiber cross-sectional area), peak stiffness, and maximal shortening velocity ( V o) of single permeabilized type I soleus muscle fibers. Adult rats were subjected to one of the following treatments: normal weight bearing (WB), non-weight bearing (NWB), or NWB with exercise treatments (NWB+Ex). The hindlimbs of the NWB and NWB+Ex rats were suspended for 14 days via tail harnesses. Four times each day, the NWB+Ex rats were removed from suspension and performed 10 climbs (∼15 cm each) up a steep grid with a 500-g mass (∼1.5 times body mass) attached to their tail harness. NWB was associated with significant reductions in type I fiber diameter, absolute force, normalized force, and stiffness. Exercise treatments during NWB attenuated the decline in fiber diameter and absolute force by almost 60% while maintaining normalized force and stiffness at WB levels. Type I fiber V oincreased by 33% with NWB and remained at this elevated level despite the exercise treatments. We conclude that in comparison to intermittent weight bearing only (J. J. Widrick, J. J. Bangart, M. Karhanek, and R. H. Fitts. J. Appl. Physiol. 80: 981–987, 1996), resistance exercise was more effective in attenuating alterations in type I soleus fiber absolute force, normalized force, and stiffness but was less effective in restoring type I fiber V oto WB levels.

Distribution of myosin heavy chain isoforms in non-weight-bearing rat soleus muscle fibers

1996 ◽  
Vol 81 (6) ◽  
pp. 2540-2546 ◽  
Author(s):  
Robert J. Talmadge ◽  
Roland R. Roy ◽  
V. Reggie Edgerton
Keyword(s):  
Myosin Heavy Chain ◽  
Soleus Muscle ◽  
Heavy Chain ◽  
De Novo ◽  
Weight Bearing ◽  
Muscle Fibers ◽  
Myosin Heavy Chain Isoforms ◽  
Hindlimb Suspension ◽  
Type I ◽  
Rat Soleus Muscle

Talmadge, Robert J., Roland R. Roy, and V. Reggie Edgerton.Distribution of myosin heavy chain isoforms in non-weight-bearing rat soleus muscle fibers. J. Appl. Physiol. 81(6): 2540–2546, 1996.—The effects of 14 days of spaceflight (SF) or hindlimb suspension (HS) (Cosmos 2044) on myosin heavy chain (MHC) isoform content of the rat soleus muscle and single muscle fibers were determined. On the basis of electrophoretic analyses, there was a de novo synthesis of type IIx MHC but no change in either type I or IIa MHC isoform proportions after either SF or HS compared with controls. The percentage of fibers containing only type I MHC decreased by 26 and 23%, and the percentage of fibers with multiple MHCs increased from 6% in controls to 32% in HS and 34% in SF rats. Type IIx MHC was always found in combination with another MHC or combination of MHCs; i.e., no fibers contained type IIx MHC exclusively. These data suggest that the expression of the normal complement of MHC isoforms in the adult rat soleus muscle is dependent, in part, on normal weight bearing and that the absence of weight bearing induces a shift toward type IIx MHC protein expression in the preexisting type I and IIa fibers of the soleus.

Coordinated changes in contractility, energetics, and isomyosins after aortic stenosis

1987 ◽  
Vol 252 (2) ◽  
pp. H275-H282
Author(s):  
Y. Lecarpentier ◽  
L. B. Bugaisky ◽  
D. Chemla ◽  
J. J. Mercadier ◽  
K. Schwartz ◽  
...  
Keyword(s):  
Cardiac Hypertrophy ◽  
Peak Power ◽  
Ventricular Hypertrophy ◽  
Left Ventricular ◽  
Ascending Aorta ◽  
Peak Power Output ◽  
Shortening Velocity ◽  
Old Rats ◽  
Quantitative Changes

To investigate possible alterations of myocardial performance in young rats, cardiac hypertrophy was induced by stenosis of the ascending aorta (AS) in three groups of 25-day-old rats that were compared with three groups of sham-operated controls (C). The cardiac overload duration was 8-10 days, 1 mo, and 2 mo in groups 1, 2, and 3, respectively. Mechanics and energetics were studied in left ventricular papillary muscles, and determination of the V1 and V3 isomyosin pattern was achieved in the same papillary muscle. The majority of quantitative changes concerning the cardiac growth process, contractility, and isomyosin shifts occurred within 8-10 days of stenosis. At this point, the degree of left ventricular hypertrophy relative to C was 53 +/- 6%, whereas maximum unloaded shortening velocity (Vmax) decreased significantly (2.8 +/- 0.1 in C vs. 1.9 +/- 0.1 Lmax/s in AS), peak power output (Emax) decreased (1.8 +/- 0.3 in C vs. 0.6 +/- 0.1 in AS), and the curvature of Hill's hyperbola increased (1.3 +/- 0.4 in C vs. 2.0 +/- 0.7 in AS); moreover, the percent V1 isomyosin decreased significantly (98 +/- 1 in C vs. 51 +/- 3% in AS) and the percent V3 isomyosin increased significantly (2 +/- 1 in C vs. 26 +/- 2% in AS). Beyond 8-10 days of AS, additional changes in cardiac hypertrophy and in mechanical and biochemical parameters were less marked.(ABSTRACT TRUNCATED AT 250 WORDS)

Peak power output is maintained in rabbit psoas and rat soleus single muscle fibers when CTP replaces ATP

1998 ◽  
Vol 85 (1) ◽  
pp. 76-83 ◽  
Author(s):  
Philip A. Wahr ◽  
Joseph M. Metzger
Keyword(s):  
Muscle Contraction ◽  
Peak Power ◽  
Muscle Length ◽  
Peak Power Output ◽  
Fiber Types ◽  
Rabbit Psoas ◽  
Cross Bridge ◽  
Chemomechanical Coupling ◽  
Velocity Relationship ◽  
Force Velocity

The chemomechanical coupling mechanism in striated muscle contraction was examined by changing the nucleotide substrate from ATP to CTP. Maximum shortening velocity [extrapolation to zero force from force-velocity relation ( V max) and slope of slack test plots ( V 0)], maximum isometric force (Po), power, and the curvature of the force-velocity curve [ a/Po(dimensionless parameter inversely related to the curvature)] were determined during maximum Ca2+-activated isotonic contractions of fibers from fast rabbit psoas and slow rat soleus muscles by using 0.2 mM MgATP, 4 mM MgATP, 4 mM MgCTP, or 10 mM MgCTP as the nucleotide substrate. In addition to a decrease in the maximum Ca2+-activated force in both fiber types, a change from 4 mM ATP to 10 mM CTP resulted in a decrease in V max in psoas fibers from 3.26 to 1.87 muscle length/s. In soleus fibers, V max was reduced from 1.94 to 0.90 muscle length/s by this change in nucleotide. Surprisingly, peak power was unaffected in either fiber type by the change in nucleotide as the result of a three- to fourfold decrease in the curvature of the force-velocity relationship. The results are interpreted in terms of the Huxley model of muscle contraction as an increase in f 1and g 1 coupled to a decrease in g 2(where f 1 is the rate of cross-bridge attachment and g 1 and g 2 are rates of detachment) when CTP replaces ATP. This adequately accounts for the observed changes in Po, a/Po, and V max. However, the two-state Huxley model does not explicitly reveal the cross-bridge transitions that determine curvature of the force-velocity relationship. We hypothesize that a nucleotide-sensitive transition among strong-binding cross-bridge states following Pi release, but before the release of the nucleotide diphosphate, underlies the alterations in a/Poreported here.

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