scholarly journals Stimulation Pattern That Maximizes Force in Paralyzed and Control Whole Thenar Muscles

2002 ◽  
Vol 87 (5) ◽  
pp. 2271-2278 ◽  
Author(s):  
Lisa Griffin ◽  
Sharlene Godfrey ◽  
Christine K. Thomas
Keyword(s):  
Short Interval ◽  
Motor Units ◽  
Muscle Stiffness ◽  
Peak Force ◽  
Single Motor Units ◽  
Time Integral ◽  
Cord Injury ◽  
Force Time ◽  
And Control ◽  
Force Time Integral

The pattern of seven pulses that elicited maximal thenar force was determined for control muscles and those that have been paralyzed chronically by spinal cord injury. For each subject group ( n = 6), the peak force evoked by two pulses occurred at a short interval (5–15 ms; a “doublet”), but higher mean relative forces were achieved in paralyzed versus control muscles (41.4 ± 3.9% vs. 22.7 ± 2.0% maximal). Thereafter, longer intervals evoked peak force in each type of muscle (mean: 35 ± 1 ms, 36 ± 2 ms, respectively). With seven pulses, paralyzed and control muscles reached 76.4 ± 5.6% and 57.0 ± 2.6% maximal force, respectively. These force differences resulted from significantly greater doublet/twitch and doublet/tetanic force ratios in paralyzed (2.73 ± 0.08, 0.35 ± 0.03) compared with control muscles (2.07 ± 0.07, 0.25 ± 0.01). The greater force enhancement produced in paralyzed muscles with two closely spaced pulses may relate to changes in muscle stiffness and calcium metabolism. Peak force-time integrals were also achieved with an initial short interpulse interval, followed by longer intervals. The postdoublet intervals that produced peak force-time integrals in paralyzed and control muscles were longer than those for peak force, however (77 ± 3 ms, 95 ± 4 ms, respectively). These data show that the pulse patterns that maximize force and force-time integral in paralyzed muscles are similar to those that maximize these parameters in single motor units and various whole muscles across species. Thus the changes in neuromuscular properties that occur with chronic paralysis do not strongly influence the pulse pattern that optimizes muscle force or force-time integral.

Plantar Loading Characteristics During Walking in Females With and Without Patellofemoral Pain

2015 ◽  
Vol 105 (1) ◽  
pp. 1-7 ◽  
Author(s):  
John D. Willson ◽  
Eric D. Ellis ◽  
Thomas W. Kernozek
Keyword(s):  
Contact Area ◽  
Patellofemoral Pain ◽  
Peak Force ◽  
First Metatarsal ◽  
Time Integral ◽  
Foot Pronation ◽  
Force Time ◽  
Arch Index ◽  
Plane Joint ◽  
Force Time Integral

Background Patellofemoral pain (PFP) is a common injury, particularly in females. Foot pronation may promote knee and hip transverse plane joint kinematics during gait thought to contribute to PFP. Greater knowledge of plantar loading characteristics in females with PFP may be valuable to provide a basis for clinical decisions regarding footwear and foot orthoses. The purpose of this study was to compare plantar loading distribution in females with and without PFP during gait. Methods Plantar pressure during walking was recorded from 19 females with PFP and 20 females without PFP. Contact area, peak force, and force-time integral were evaluated in ten plantar areas. Arch index was also calculated from contact area data during gait. Results Contact area in females with PFP was 9% smaller in the first metatarsal region (P = .039) and 20% smaller in the midfoot region (P = .042) than in females without PFP. Peak force was 31% lower in the midfoot region for females with PFP (P = .027) and 13% lower in the first metatarsal region (P = .064). Force-time integral was 18% lower in the first metatarsal region in females with PFP (P = .024). Females with PFP demonstrated a lower arch index (suggesting a higher arch) (P = .028). Conclusions Decreased medial forefoot loading and decreased midfoot contact suggest decreased foot pronation during gait in females with PFP relative to females without PFP. Decreased foot pronation may foster increased patellofemoral joint loading rates. These data contribute to rationale for footwear modifications to modify plantar loading characteristics in people experiencing PFP.

scholarly journals Human-In-The-Loop Optimization of A Wearable Robot Using Foot Pressure Sensors

2021 ◽  
Author(s):  
Micheal Jacobson ◽  
Prakyath Kantharaju ◽  
Hyeongkeun Jeong ◽  
Xingyuan Zhou ◽  
Jae-Kwan Ryu ◽  
...  
Keyword(s):  
Cost Function ◽  
Metabolic Cost ◽  
Wearable Robot ◽  
Foot Pressure ◽  
Physical Effort ◽  
Foot Force ◽  
Time Integral ◽  
Force Time ◽  
And Control ◽  
Force Time Integral

Abstract Background: Individuals with below-knee amputation (BKA) experience increased physical effort when walking, and the use of a robotic ankle-foot prosthesis (AFP) can reduce such effort. Our prior study on a robotic AFP showed that walking effort could be reduced if the robot is personalized to the wearer. The personalization is accomplished using human-in-the-loop (HIL) optimization, in which the cost function is based on a real-time physiological signal indicating physical effort. The conventional physiological measurement, however, requires a long estimation time, hampering real-time optimization due to the limited experimental time budget. In addition, the physiological sensor, based on respiration uses a mask with rigid elements that may be difficult for the wearer to use. Prior studies suggest that a symmetry measure using a less intrusive sensor, namely foot pressure, could serve as a metric of gait performance. This study hypothesized that a function of foot pressure, the symmetric foot force-time integral, could be used as a cost function to rapidly estimate the physical effort of walking; therefore, it can be used to personalize assistance provided by a robotic ankle in a HIL optimization scheme. Methods: We developed a new cost function derived from a well-known clinical measure, the symmetry index, by hypothesizing that foot force-time integral (FFTI) symmetry would be highly correlated with metabolic cost. We conducted experiments on human participants (N = 8) with simulated amputation to test the new cost function. The study consisted of a discrete trial day, an HIL optimization training day, and an HIL optimization data collection day. We used the discrete trial day to evaluate the correlation between metabolic cost and a cost function using symmetric FFTI percentage. During walking, we varied the prosthetic ankle stiffness while measuring foot pressure and metabolic rate. On the second and third days, HIL optimization was used to find the optimal stiffness parameter with the new cost function using symmetric FFTI percentage. Once the optimal stiffness parameter was found, we validated the performance with comparison to a weight-based stiffness and control-off conditions. We measured symmetric FFTI percentage during the stance phase, prosthesis push-off work, metabolic cost, and user comfort in each condition. We expected the optimized prosthetic ankle stiffness based on the newly developed cost function could reduce the energy expenditure during walking for the individuals with simulated amputation. Results: We found that the cost function using symmetric foot force-time integral percentage presents a reasonable correlation with measured metabolic cost (Pearson’s R > 0.62). When we employed the new cost function in HIL ankle-foot prosthesis parameter optimization, 8 individuals with simulated amputation reduced their cost of walking by 15.9% (p = 0.01) and 16.1% (p = 0.02) compared to the weight-based and control-off conditions, respectively. The symmetric FFTI percentage for the optimal condition tended to be closer to the ideal symmetry value (50%) compared to weight-based (p = 0.23) and control-off conditions (p = 0.04). Conclusion: This study suggests that foot force-time integral symmetry using foot pressure sensors can be used as a cost function when optimizing a wearable robot parameter.

Fatigue of Paralyzed and Control Thenar Muscles Induced by Variable or Constant Frequency Stimulation

2003 ◽  
Vol 89 (4) ◽  
pp. 2055-2064 ◽  
Author(s):  
Christine K. Thomas ◽  
Lisa Griffin ◽  
Sharlene Godfrey ◽  
Edith Ribot-Ciscar ◽  
Jane E. Butler
Keyword(s):  
Spinal Cord ◽  
High Frequency ◽  
Low Frequency ◽  
Constant Frequency ◽  
Time Integral ◽  
Frequency Stimulation ◽  
Force Time ◽  
And Control ◽  
Frequency Pulse ◽  
Force Time Integral

Muscles paralyzed by chronic (>1 yr) spinal cord injury fatigue readily. Our aim was to evaluate whether the fatigability of paralyzed thenar muscles ( n = 10) could be reduced by the repeated delivery of variable versus constant frequency pulse trains. Fatigue was induced in four ways. Intermittent supramaximal median nerve stimulation (300-ms-duration trains) was delivered at 1) constant high frequency (13 pulses at 40 Hz each second for 2 min); 2) variable high frequency (each second for 2 min). The first two intervals of each variable frequency train were 5 and 20 ms. The remaining pulses were evenly distributed in time across 275 ms. The number of pulses varied for each subject such that the force time integral in the unfatigued state matched that evoked by a constant 40-Hz train; 3) constant low frequency (7 pulses at 20 Hz each second for 4 min); and 4) variable low frequency (each second for 4 min). The pulse pattern was the same as that for variable high frequency except that the force-time integral was matched to that produced by the constant low-frequency stimulation. These same experiments were performed on the thenar muscles of five able-bodied control subjects. The variable high-frequency trains used to fatigue paralyzed and control muscles had an average (± SE) of 12 ± 2 and 10 ± 1 pulses, respectively. Variable low-frequency trains had 7 ± 1 and 6 ± 1 pulses, respectively. Significant mean force declines of comparable magnitude (to 20–25% initial fatigue force or to 13–21% initial 50 Hz force) were seen in paralyzed muscles with all four stimulation protocols. The force reductions in paralyzed muscles were always accompanied by significant increases in half-relaxation time and decreases in force-time integral, irrespective of the stimulation protocol. Significant force decreases also occurred in control muscles during each fatigue test. Again, these force declines were similar whether constant or variable pulse patterns were used at high or low frequencies (to 40–60% initial fatigue force or to 29–36% initial 50 Hz force). The force reductions in control muscles were significantly less than those seen in paralyzed muscles, except when constant high-frequency stimulation was used. The variations in stimulation frequency, pulse pattern, and pulse number used in this study therefore had little influence on thenar muscle fatigue in control subjects or in spinal cord–injured subjects with chronic paralysis.

scholarly journals Progressive recruitment of muscle fibers is not necessary for the slow component of V̇o2 kinetics

2008 ◽  
Vol 105 (2) ◽  
pp. 575-580 ◽  
Author(s):  
Jerzy A. Zoladz ◽  
L. Bruce Gladden ◽  
Michael C. Hogan ◽  
Zenon Nieckarz ◽  
Bruno Grassi
Keyword(s):  
Slow Component ◽  
Muscle Fibers ◽  
Constant Load ◽  
Peak Force ◽  
Time Integral ◽  
V̇o2 Kinetics ◽  
Force Time ◽  
Kinetics Of ◽  
Force Time Integral

The “slow component” of O2 uptake (V̇o2) kinetics during constant-load heavy-intensity exercise is traditionally thought to derive from a progressive recruitment of muscle fibers. In this study, which represents a reanalysis of data taken from a previous study by our group (Grassi B, Hogan MC, Greenhaff PL, Hamann JJ, Kelley KM, Aschenbach WG, Constantin-Teodosiu D, Gladden LB. J Physiol 538: 195–207, 2002) we evaluated the presence of a slow component-like response in the isolated dog gastrocnemius in situ ( n = 6) during 4 min of contractions at ∼60–70% of peak V̇o2. In this preparation all muscle fibers are maximally activated by electrical stimulation from the beginning of the contraction period, and no progressive recruitment of fibers is possible. Muscle V̇o2 was calculated as blood flow multiplied by arteriovenous O2 content difference. The muscle fatigued (force decreased by ∼20–25%) during contractions. Kinetics of adjustment were evaluated for 1) V̇o2, uncorrected for force development; 2) V̇o2 normalized for peak force; 3) V̇o2 normalized for force-time integral. A slow component-like response, described in only one muscle out of six when uncorrected V̇o2 was considered, was observed in all muscles when V̇o2/peak force and V̇o2/force-time were considered. The amplitude of the slow component-like response, expressed as a fraction of the total response, was higher for V̇o2/peak force (0.18 ± 0.06, means ± SE) and for V̇o2/force-time (0.22 ± 0.05) compared with uncorrected V̇o2 (0.04 ± 0.04). A progressive recruitment of muscle fibers may not be necessary for the development of the slow component of V̇o2 kinetics, which may be caused by the metabolic factors that induce muscle fatigue and, as a consequence, reduce the efficiency of muscle contractions.

Skeletal Muscle Specific Calpastatin Overexpression Mitigates Muscle Weakness in Aging and Extends Lifespan

2021 ◽  
Author(s):  
Elizabeth A. Schroder ◽  
Lin Wang ◽  
Yuan Wen ◽  
Leigh Ann P. Callahan ◽  
Gerald S. Supinski
Keyword(s):  
Skeletal Muscle ◽  
Peak Force ◽  
Force Frequency ◽  
Time Integral ◽  
Potential Contributor ◽  
Force Time ◽  
Aging Muscle ◽  
And Function ◽  
The Impact ◽  
Force Time Integral

Calpain activation has been postulated as a potential contributor to the loss of muscle mass and function associated with both aging and disease but limitations of previous experimental approaches have failed to completely examine this issue. We hypothesized that mice overexpressing calpastatin, an endogenous inhibitor of calpain (CalpOX), solely in skeletal muscle would show an amelioration of the aging muscle phenotype. We assessed 4 groups of mice (age in months): (1) young wild type (5.71±0.43) (WT); (2) young CalpOX (5.6±0.5); (3) old WT (25.81±0.56); and (4) old CalpOX (25.91±0.60) for diaphragm and limb muscle (extensor digitorum longus, EDL) force frequency relations. Aging significantly reduced diaphragm and EDL peak force in old WT mice, and decreased the force-time integral during a fatiguing protocol by 48% and 23% in aged WT diaphragm and EDL, respectively. In contrast, we found that CalpOX mice had significantly increased diaphragm and EDL peak force in old mice, similar to that observed in young mice. The impact of aging on the force-time integral during a fatiguing protocol was abolished in the diaphragm and EDL of old CalpOX animals. Surprisingly, we found that CalpOX had a significant impact on longevity, increasing median survival from 20.55 months in WT mice to 24 months in CalpOX mice (p = 0.0006).

scholarly journals Force-time integral decreases with ejection despite constant oxygen consumption and pressure-volume area in dog left ventricle.

1987 ◽  
Vol 60 (6) ◽  
pp. 797-803 ◽  
Author(s):  
H Suga ◽  
Y Goto ◽  
T Nozawa ◽  
Y Yasumura ◽  
S Futaki ◽  
...  
Keyword(s):  
Oxygen Consumption ◽  
Left Ventricle ◽  
Time Integral ◽  
Force Time ◽  
Force Time Integral

The Effect of Muscle Lentgh on Force-Time Integral in Relation to Energy-Rich Phosphate Consumption

1985 ◽  
pp. 605-610 ◽  
Author(s):  
A. De Haan ◽  
J. E. Van Doorn ◽  
P. A. Huijing ◽  
R. D. Woittiez ◽  
H. G. Westra
Keyword(s):  
Time Integral ◽  
Force Time ◽  
Force Time Integral

Regulation of energy consumption in cardiac muscle: analysis of isometric contractions

1999 ◽  
Vol 276 (3) ◽  
pp. H998-H1011 ◽  
Author(s):  
Amir Landesberg ◽  
Samuel Sideman
Keyword(s):  
Energy Consumption ◽  
Cardiac Muscle ◽  
Feedback Mechanism ◽  
Isometric Contractions ◽  
Cross Bridge ◽  
Time Integral ◽  
Length Relationship ◽  
Cross Bridges ◽  
Force Time ◽  
Force Time Integral

The well-known linear relationship between oxygen consumption and force-length area or the force-time integral is analyzed here for isometric contractions. The analysis, which is based on a biochemical model that couples calcium kinetics with cross-bridge cycling, indicates that the change in the number of force-generating cross bridges with the change in the sarcomere length depends on the force generated by the cross bridges. This positive-feedback phenomenon is consistent with our reported cooperativity mechanism, whereby the affinity of the troponin for calcium and, hence, cross-bridge recruitment depends on the number of force-generating cross bridges. Moreover, it is demonstrated that a model that does not include a feedback mechanism cannot describe the dependence of energy consumption on the loading conditions. The cooperativity mechanism, which has been shown to determine the force-length relationship and the related Frank-Starling law, is shown here to provide the basis for the regulation of energy consumption in the cardiac muscle.

Preload does not influence nonmechanical O2 consumption in isolated rabbit heart

1994 ◽  
Vol 266 (3) ◽  
pp. H1047-H1054 ◽  
Author(s):  
A. Higashiyama ◽  
M. W. Watkins ◽  
Z. Chen ◽  
M. M. LeWinter
Keyword(s):  
Energy Consumption ◽  
Diastolic Pressure ◽  
Rabbit Heart ◽  
Left Ventricular ◽  
Energetic Cost ◽  
O2 Consumption ◽  
Time Integral ◽  
Force Time ◽  
Whole Heart ◽  
Force Time Integral

Myocardial energy consumption for nonmechanical activity (excitation-contraction coupling) has been shown to be length dependent in isolated muscle studies but no more than minimally affected by preload in the whole heart. However, unloaded O2 consumption (VO2, which is used to estimate nonmechanical VO2 in whole heart) may not be accurate for quantifying nonmechanical energy consumption, because it contains VO2 for residual cross-bridge cycling. To more accurately determine the influence of left ventricular (LV) diastolic volume on nonmechanical VO2 in whole heart, we employed a new method for quantifying nonmechanical VO2, using the drug 2,3-butanedione monoxime (BDM). We measured VO2 and force-time integral during infusion of BDM (< or = 5 mM) at high (VH) and low LV volumes (VL) in 16 excised isovolumically contracting red blood cell-perfused rabbit ventricles. LV end-diastolic pressure was 9.7 +/- 4.6 and 3.8 +/- 2.8 (SD) mmHg at VH and VL, respectively. Nonmechanical VO2, estimated as the VO2-axis intercept of the linear VO2-force-time integral relation obtained during BDM infusion, did not differ significantly between VH and VL (0.0137 +/- 0.0083 and 0.0132 +/- 0.0090 ml O2.beat-1 x 100 gLV-1, P = 0.702). A multiple linear regression analysis for the pooled data confirmed this finding (P = 0.361). We conclude that, in the rabbit heart, LV diastolic volume does not importantly affect nonmechanical energy consumption over a physiological range of LV end-diastolic pressure. This indicates that length-dependent activation does not have an energetic cost in whole rabbit heart and suggests that its predominant mechanism is increased Ca2+ affinity for the contractile proteins.

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