Biomedical subjects

Stuart A Binder-Macleod

Publications and source records attributed to Stuart A Binder-Macleod.

13 recordsLinked to original sources

PubMed2003

Predictability of maximum voluntary isometric knee extension force from submaximal contractions in older adults.

The purposes of this study were to develop and test a model describing the relationship between the central activation ratio (CAR; a measure of voluntary muscle activation) and percent maximum voluntary contraction (%MVC) force for old adults and to provide a method for more accurate determination of voluntary muscle activation failure. Twenty-one adults (ages 64-81) performed isometric testing of the quadriceps at 25%, 50%, 75%, and 100% MVC. During each contraction, a 100-HZ, 120-ms train of electrical pulses was delivered to the quadriceps muscle to quantify voluntary muscle activation. Similar to a young, healthy population (ages 20-35), a curvilinear relationship existed between the CAR and %MVC force for older adults. Predictions of subjects' MVCs using the linear model of CAR-%MVC force relationship generally demonstrated poor agreement with actual MVCs. Predictions of MVC from submaximal contractions (25%, 50%, and 75%) using a previously identified curvilinear young adult CAR-%MVC relationship were good [ICC (2,1): 0.81, 0.96, and 0.82, respectively]. Similar agreement was obtained from the curvilinear older adult CAR-%MVC relationship. These data suggest that the CAR-%MVC relationship is similar in young and older adult subjects and that curvilinear models of this relationship can predict MVC forces in older adults more accurately. Reexamination of the relationship between the CAR and %MVC force may allow a more accurate determination of how failure of voluntary muscle activation contributes to weakness in old adults.

Adult↗

PubMed2003

Are voluntary muscle activation deficits in older adults meaningful?

The relationship between the central activation ratio (CAR) and contraction force is curvilinear, not linear as was previously believed. Voluntary quadriceps femoris muscle activation from previously collected data sets in 46 older adults (64-84 years) and 46 young adults (18-32 years) were therefore reexamined using a curvilinear model of the voluntary muscle activation-percent maximum voluntary force relationship. This method revealed lower voluntary muscle activation in older adults (0.868 +/- 0.018) than younger subjects (0.978 +/- 0.005). The mean difference between older and younger adults was 11%, which may be more meaningful than previous reports of 2-4% because it could explain the greater rate of strength loss as compared to loss of muscle mass as humans age.

Adolescent↗

PubMed2003

Effect of potentiation on the catchlike property of human skeletal muscles.

The catchlike property of skeletal muscle is the force enhancement produced when a brief, high-frequency burst of pulses (two to four pulses) is added to a subtetanic train of pulses. Stimulation trains that take advantage of the catchlike property have been shown to produce greater forces than trains commonly used during clinical application of functional electrical stimulation (FES). We recently showed, however, that there was no force enhancement observed with the catchlike property when muscles were nonfatigued and highly potentiated. Thus, understanding the relationship between the force augmentations produced by the catchlike property and potentiation may provide insight into the physiological conditions that best take advantage of the catchlike property. The goal of this study was to explore quantitatively the effect of potentiation on the catchlike property of the muscle. Isometric data were collected from human quadriceps femoris muscles. A negative linear relationship between the force augmentation produced by the catchlike property and the amount of potentiation was observed. These data showed that for nonfatigued muscles, the catchlike property would be most beneficial at the onset of activation, when muscles are the least potentiated. These results should help to guide clinicians to design stimulation protocols that optimize performance during FES.

Adult↗

PubMed2003

Changing stimulation patterns improves performance during electrically elicited contractions.

The clinical efficacy of functional electrical stimulation (FES) is limited by the rapid onset of fatigue. FES applications use electrical stimuli separated by regular interpulse intervals (constant-frequency trains or CFTs) to activate muscles. However, doublet-frequency trains (DFTs) may produce greater forces than CFTs, but also produce more fatigue. DFTs contain a series of doublets, two pulses separated by a short (5-ms) interpulse interval. We hypothesized that a combination of CFTs followed by DFTs would improve performance compared to either train type alone. Quadriceps muscles of 15 normal subjects were fatigued with either 150 DFTs, or initially fatigued with CFTs until the targeted isometric force was no longer produced and then switched to DFTs. The combination reached the targeted isometric force (mean +/- SEM) more times (59.80 +/- 4.03) than either the CFTs alone (51.20 +/- 3.50) or DFTs alone (55.33 +/- 3.81). This finding suggests that combining train types may be a useful strategy to offset the rapid fatigue that persons with neurological dysfunction, such as spinal cord injury, experience when using FES.

Adult↗

PubMed2002

Electrical stimulation factors in potentiation of human quadriceps femoris.

Potentiation is the enhancement of force seen after repetitive activation of skeletal muscle. The frequency and duration of stimulation, total number of pulses delivered to the muscle, and the peak forces or force-time integrals produced by the stimulation all have been suggested to affect the degree of potentiation. The purpose of this study was to determine the effect of the electrical stimulation characteristics on the development of post-activation potentiation. Eleven subjects were tested with five potentiating trains, including 12-pulse 100-HZ, 31-HZ, 14-HZ, and 5-HZ, and 6-pulse 14-HZ trains. The potentiating trains differed in stimulation frequency, train duration, and total number of pulses. They also produced different peak forces and force time integrals from the activated muscles. Our results showed that the 12-pulse 5-HZ train produced about 50% less potentiation than the other four potentiating trains. At stimulation frequencies of 14 HZ or higher, the total number of pulses delivered to the muscle was the primary factor in potentiation development. Furthermore, peak force and force-time integral had no effects on the rate or amount of potentiation. These results should help clinicians and researchers to design protocols that control for the effects of muscle potentiation.

Adult↗

PubMed2002

A mathematical model that predicts the force-frequency relationship of human skeletal muscle.

In previous work we developed and validated a mathematical model that predicted force output from skeletal muscles subjected to six-pulse stimulation trains under isometric condition. The current study investigated the model's ability to predict force responses to longer stimulation trains under both nonfatigued and fatigued conditions. Using the six-pulse train model to predict the force produced by longer stimulation trains showed that the model was successful, but a modified parameter identification scheme was required. For most of the trains tested the model accounted for 95% of the variance in the experimental forces produced by stimulation trains, with mean frequencies from 12.5 to 100 HZ, train durations from 485 to 1000 ms, and number of pulses from 14 to 50 for both nonfatigued and fatigued muscles. The success of our mathematical model in predicting forces produced by stimulations with a wide range of frequencies, durations, and number of pulses implies great potential of the model for the identification of optimal activation patterns that should be used during functional electrical stimulation.

Actins↗

PubMed2002

Modeling the length dependence of isometric force in human quadriceps muscles.

Functional electrical stimulation is used to restore movement and function of paralyzed muscles by activating skeletal muscle artificially. An accurate and predictive mathematical model can facilitate the design of stimulation patterns that produce the desired force. The present study is a first step in developing a mathematical model for non-isometric muscle contractions. The goals of this study were to: (1) identify how our isometric force model's parameters vary with changes in knee joint angle, (2) identify the best knee flexion angle to parameterize this model, and (3) validate the model by comparing experimental data to predictions in response to a wide range of stimulation frequencies and muscle lengths. Results showed that by parabolically varying one of the free parameters with knee joint angle and fixing the other parameters at the values identified at 40 degrees of knee flexion, the model could predict the force responses to a wide range of stimulation frequencies and patterns at different muscle lengths. This work showed that the current isometric force model is capable of predicting the changes in skeletal muscle force at different muscle lengths.

Biomechanical Phenomena↗

PubMed2002

A predictive fatigue model--I: Predicting the effect of stimulation frequency and pattern on fatigue.

Previously we developed a mathematical force- and fatigue-model system that could predict fatigue produced by a wide range of frequencies and pulse patterns. However, the models tended to overestimate the forces produced by higher frequency trains. This paper presents modifications to our previously developed force- and fatigue-model system to improve the accuracy in predicting forces during repetitive activation of human skeletal muscle. By comparing the predictions produced by the modified force and fatigue models to those by our previous models, the modification appears to be successful. The current force- and fatigue-model system accounts for about 93% variance in experimental data produced by fatigue protocols consisting of trains with a wide range of frequencies and pulse patterns. In addition, the present models successfully predict the effect of stimulation frequency and pulse pattern on muscle fatigue. The success of our current force- and fatigue-model system suggests its potential use in helping to identify the optimal activation pattern to use during the clinical application of functional electrical stimulation.

Algorithms↗

PubMed2002

A predictive fatigue model--II: Predicting the effect of resting times on fatigue.

We have recently developed a force- and fatigue-model system that accurately predicted the effect of stimulation frequency on muscle fatigue. The data used to test the model were produced by stimulation trains with resting times of 500 ms. Because the resting times between stimulation trains affect muscle fatigue, this study tested the model's ability to predict the effect of resting times on fatigue. In addition, because this study included different subjects than those used to develop the model, the validity of the model could be tested. Data were collected from human quadriceps femoris muscles using fatigue protocols that included resting times of 500, 750, or 1000 ms. Our results showed that the model predicted fatigue as being a decreasing function of resting time, which was consistent with experimental data. Reliability tests between the experimental data and predictions showed interclass correlation coefficients of 0.97, 0.95, and 0.81 for the initial, final, and percentage decline in peak forces, respectively, suggesting strong agreement between the experimental data and the predictions by the model. The success of our current force- and fatigue-model system helps to validate the model and suggests its potential use in identifying the optimal activation pattern during clinical application of functional electrical stimulation.

Algorithms↗

PubMed2002

Metabolic costs of isometric force generation and maintenance of human skeletal muscle.

During isometric contractions, no true work is performed, so the force-time integral (FTI) is often used to approximate isometric work. However, the relationship between FTI and metabolic cost is not as linear. We tested the hypothesis that this nonlinearity was due to the cost of attaining a given force being greater than that of maintaining it. The ATP consumed per contraction in the human medial gastrocnemius muscle (n = 6) was determined by use of (31)P-NMR spectroscopy during eight different electrical stimulation protocols. Each protocol consisted of 8 trains of a single frequency (20 or 80 Hz) and duration (300, 600, 1,200, or 1,800 ms) performed under ischemic conditions. The cost of force generation was determined from the ATP turnover during the short-duration trains that did not attain a steady force level. Estimates of the cost of force maintenance at each frequency were determined by subtracting the ATP turnover during the shorter-duration trains from the turnover during the long-duration trains. The force generation phase of an isometric contraction was indeed more metabolically costly than the force maintenance phase during both 20- and 80-Hz stimulation. Thus the mean rate of ATP hydrolysis appeared to decline as contraction duration increased. Interestingly, the metabolic costs of maintaining force during 20-Hz and 80-Hz stimulation were comparable, although different levels of force were produced.

Adenosine Triphosphate↗

PubMed2002

Effects of stimulation frequencies and patterns on performance of repetitive, nonisometric tasks.

The purpose of this paper was to determine the effects of stimulation pattern and frequency on repetitive human knee movements. Quadriceps femoris muscles were stimulated against a load equal to 10% of each subject's maximum voluntary isometric force. The main variable of interest was the number of repetitions in which the leg reached a target angle of 40 degrees of knee extension. Sixteen different trains were tested, including 1) six constant-frequency trains with frequencies ranging from 9 to 100 Hz, 2) five variable-frequency trains with an initial 5-ms triplet and mean frequencies ranging from 11 to 35 Hz, and 3) five doublet-frequency trains, which used doublets (2 pulses with a 5-ms interpulse interval) to replace single pulses, with mean frequencies of 17-57 Hz. Testing was stopped when the subject failed to reach the target angle for three consecutive activations. Results showed that no single pattern was best for all subjects. The 33- and 100-Hz constant-frequency trains, 35-Hz variable-frequency trains, and 27- and 36-Hz doublet frequency trains each met the target the most times for some subjects. The results showed that, under our testing conditions, higher frequency trains were better suited for producing repetitive knee movements than lower frequency trains.

Adult↗

PubMed2002

Effects of muscle activation on fatigue and metabolism in human skeletal muscle.

Increasing stimulation frequency has been shown to increase fatigue but not when the changes in force associated with changes in frequency have been controlled. An effect of frequency, independent of force, may be associated with the metabolic cost resulting from the additional activations. Here, two separate experiments were performed on human medial gastrocnemius muscles. The first experiment (n = 8) was designed to test the effect of the number of pulses on fatigue. The declines in force during two repetitive, 150-train stimulation protocols that produced equal initial forces, one using 80-Hz trains and the other using 100-Hz trains, were compared. Despite a difference of 600 pulses (23.5%), the protocols produced similar rates and amounts of fatigue. In the second experiment, designed to test the effect of the number of pulses on the metabolic cost of contraction, 31P-NMR spectra were collected (n = 6) during two ischemic, eight-train stimulation protocols (80- and 100-Hz) that produced comparable forces despite a difference of 320 pulses (24.8%). No differences were found in the changes in P(i) concentration, phosphocreatine concentration, and intracellular pH or in the ATP turnover produced by the two trains. These results suggest that the effect of stimulation frequency on fatigue is related to the force produced, rather than to the number of activations. In addition, within the range of frequencies tested, increasing total activations did not increase metabolic cost.

Adenosine Triphosphate↗

PubMed2002

Factors in fatigue during intermittent electrical stimulation of human skeletal muscle.

During an electrically elicited isometric contraction, the metabolic cost of attaining is greater than of maintaining force. Thus fatigue produced during such stimulation may not simply be a function of the force-time integral (FTI), as previously suggested. The goal of the present study was to evaluate fatigue produced in human medial gastrocnemius by intermittent, isometric electrical stimulation with trains of different frequencies (20, 40, or 80 Hz) and durations (300, 600, or 1,200 ms) that produced different peak forces and FTIs. Each subject (n = 10) participated in a total of six sessions. During each session, subjects received a pre- and postfatigue testing protocol and a different, 150-train fatiguing protocol. Each fatiguing protocol used only a single frequency and duration. The fatigue produced by the different protocols was correlated to the initial peak force of the fatiguing protocols (r2= 0.74-0.85) but not to the initial or total FTI. All of the protocols tested produced a proportionately greater impairment of force in response to low- vs. high-frequency stimulation (i.e., low-frequency fatigue). There was no effect of protocol on low-frequency fatigue, suggesting that all the protocols produced comparable levels of impairment in excitation-contraction coupling. These results suggest that, for brief stimulated contractions, peak force is a better predictor of fatigue than FTI, possibly because of the different metabolic demands of attaining and maintaining force.

Adult↗