Shortening-induced depression of voluntary force in unfatigued and fatigued human adductor pollicis muscle

2003 ◽  
Vol 94 (1) ◽  
pp. 69-74 ◽  
Author(s):  
C. J. De Ruiter ◽  
A. De Haan
Keyword(s):  
Isometric Force ◽  
Experimental Studies ◽  
Adductor Pollicis ◽  
Voluntary Activation ◽  
Adductor Pollicis Muscle ◽  
Force Depression ◽  
Fatigued Muscle ◽  
Force Velocity ◽  
Shortening Contractions

The goals of this study were to investigate adductor pollicis muscle ( n = 7) force depression after maximal electrically stimulated and voluntarily activated isovelocity (19 and 306°/s) shortening contractions and the effects of fatigue. After shortening contractions, redeveloped isometric force was significantly ( P < 0.05) depressed relative to isometric force obtained without preceding shortening. For voluntarily and electrically stimulated contractions, relative force deficits respectively were (means ± SE) 25.0 ± 3.5 and 26.6 ± 1.9% (19°/s), 7.8 ± 2.2 and 11.5 ± 0.6% (306°/s), and 23.9 ± 4.4 and 31.6 ± 4.7% (19°/s fatigued). The relative force deficit was significantly smaller after fast compared with slow shortening contractions, whereas activation manner and fatigue did not significantly affect the deficit. It was concluded that in unfatigued and fatigued muscle the velocity-dependent relative force deficit was similar with maximal voluntary activation and electrical stimulation. These findings have important implications for experimental studies of force-velocity relationships. Moreover, if not accounted for in muscle models, they will contribute to differences observed between the predicted and the actually measured performance during in vivo locomotion.

Effect of airway inflammation on smooth muscle shortening and contractility in guinea pig trachealis

1993 ◽  
Vol 265 (6) ◽  
pp. L549-L554 ◽  
Author(s):  
R. W. Mitchell ◽  
I. M. Ndukwu ◽  
K. Arbetter ◽  
J. Solway ◽  
A. R. Leff
Keyword(s):  
Smooth Muscle ◽  
Guinea Pig ◽  
Neurogenic Inflammation ◽  
Isometric Force ◽  
Electrical Field Stimulation ◽  
Shortening Velocity ◽  
Lever System ◽  
Force Velocity

We studied the effect of either 1) immunogenic inflammation caused by aerosolized ovalbumin or 2) neurogenic inflammation caused by aerosolized capsaicin in vivo on guinea pig tracheal smooth muscle (TSM) contractility in vitro. Force-velocity relationships were determined for nine epithelium-intact TSM strips from ovalbumin-sensitized (OAS) vs. seven sham-sensitized controls and TSM strips for seven animals treated with capsaicin aerosol (Cap-Aer) vs. eight sham controls. Muscle strips were tethered to an electromagnetic lever system, which allowed isotonic shortening when load clamps [from 0 to maximal isometric force (Po)] were applied at specific times after onset of contraction. Contractions were elicited by supramaximal electrical field stimulation (60 Hz, 10-s duration, 18 V). Optimal length for each muscle was determined during equilibration. Maximal shortening velocity (Vmax) was increased in TSM from OAS (1.72 +/- 0.46 mm/s) compared with sham-sensitized animals (0.90 +/- 0.15 mm/s, P < 0.05); Vmax for TSM from Cap-Aer (0.88 +/- 0.11 mm/s) was not different from control TSM (1.13 +/- 0.08 mm/s, P = NS). Similarly, maximal shortening (delta max) was augmented in TSM from OAS (1.01 +/- 0.15 mm) compared with sham-sensitized animals (0.72 +/- 0.14 mm, P < 0.05); delta max for TSM from Cap-Aer animals (0.65 +/- 0.11 mm) was not different from saline aerosol controls (0.71 +/- 0.15 mm, P = NS). We demonstrate Vmax and delta max are augmented in TSM after ovalbumin sensitization; in contrast, neurogenic inflammation caused by capsaicin has no effect on isolated TSM contractility in vitro. These data suggest that airway hyperresponsiveness in vivo that occurs in association with immunogenic or neurogenic inflammation may result from different effects of these types of inflammation on airway smooth muscle.

scholarly journals Muscle fatigue examined at different temperatures in experiments on intact mammalian (rat) muscle fibers

2009 ◽  
Vol 106 (2) ◽  
pp. 378-384 ◽  
Author(s):  
H. Roots ◽  
G. Ball ◽  
J. Talbot-Ponsonby ◽  
M. King ◽  
K. McBeath ◽  
...  
Keyword(s):  
Muscle Fatigue ◽  
Power Output ◽  
Force Depression ◽  
Output Force ◽  
Different Temperatures ◽  
Force Velocity ◽  
C 30 ◽  
C 50 ◽  
Shortening Contractions

In experiments on small bundles of intact fibers from a rat fast muscle, in vitro, we examined the decline in force in repeated tetanic contractions; the aim was to characterize the effect of shortening and of temperature on the initial phase of muscle fatigue. Short tetanic contractions were elicited at a control repetition rate of 1/60 s, and fatigue was induced by raising the rate to 1/5 s for 2–3 min, both in isometric mode (no shortening) and in shortening mode, in which each tetanic contraction included a ramp shortening at a standard velocity. In experiments at 20°C ( n = 12), the force decline during a fatigue run was 25% in the isometric mode but was significantly higher (35%) in the shortening mode. In experiments at different temperatures (10–30°C, n = 11), the tetanic frequency and duration were adjusted as appropriate, and for shortening mode, the velocity was adjusted for maximum power output. In isometric mode, fatigue of force was significantly less at 30°C (∼20%) than at 10°C (∼30%); the power output (force × velocity) was >10× higher at 30°C than at 10°C, and power decline during a fatigue run was less at 30°C (∼20–30%) than at 10°C (∼50%). The finding that the extent of fatigue is increased with shortening contractions and is lower at higher temperatures is consistent with the view that force depression by inorganic phosphate, which accumulates within fibers during activity, may be a primary cause of initial muscle fatigue.

Similar effects of cooling and fatigue on eccentric and concentric force-velocity relationships in human muscle

2001 ◽  
Vol 90 (6) ◽  
pp. 2109-2116 ◽  
Author(s):  
C. J. De Ruiter ◽  
A. De Haan
Keyword(s):  
Isometric Force ◽  
Human Muscle ◽  
Muscle Temperature ◽  
Adductor Pollicis Muscle ◽  
Concentric Contractions ◽  
Cycling Rate ◽  
Concentric Force ◽  
Cross Bridge ◽  
Different Temperatures ◽  
Force Velocity

The purpose of this study was to investigate the effects of muscle temperature and fatigue during stretch (eccentric) and shortening (concentric) contractions of the maximally electrically activated human adductor pollicis muscle. After immersion of the lower arm in water baths of four different temperatures, the calculated muscle temperatures were 36.8, 31.6, 26.6, and 22.3°C. Normalized (isometric force = 100%) eccentric force increased with stretch velocity to maximal values of 136.4 ± 1.6 and 162.1 ± 2.0% at 36.8 and 22.3°C, respectively. After repetitive ischemic concentric contractions, fatigue was less at the lower temperatures, and at all temperatures the loss of eccentric force was smaller than the loss of isometric and concentric force. Consequently, normalized eccentric forces increased during fatigue to 159.7 ± 4.6 and 185.7 ± 7.3% at 36.8 and 22.3°C, respectively. Maximal normalized eccentric force increased exponentially ( r 2 = 0.95) when V max was reduced by cooling and/or fatiguing contractions. This may indicate that a reduction in cross-bridge cycling rate could underlie the significant increases in normalized eccentric force found with cooling and fatigue.

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