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Biomedical subjects

J S Petrofsky

Publications and source records attributed to J S Petrofsky.

At least 19 recordsLinked to original sources
PubMed2004

Joint acceleration during gait in relation to age.

Forty-four male and female subjects with no history of falling and whose ages ranged from 10 to 68 years participated in a series of experiments to assess movement at the joints during gait while walking in a straight line, in pivot turns and in turns of 0.33 and 0.66 m diameter. Acceleration at the joints in the forward and side-to-side direction was measured by dual-axis accelerometers placed at the ankles, knees, hips, shoulders, and on the head. Eye movement was assessed from electrodes placed on the sides of the eyes. The results of the experiments showed that for people whose age was above 40 years, significant increases in the forward-back and side-to-side movements occurred at all joints and progressively increased with age. By age 60, adverse movement of the joints as much as quadrupled in many subjects when compared to people whose age was 20-30 years. The increase in joint acceleration occurred equally in the front-back and side-to-side planes. The mechanism of the increased joint movement may be due to tendon laxness, peripheral neuropathy or loss of central control of gait due to age. Accelerometry may be a much more sensitive technique to analyze abnormalities in gait than standard video or observational gait analysis. Results are given as mean (SD) unless otherwise stated.

Acceleration↗
PubMed2003

New algorithm to control a cycle ergometer using electrical stimulation.

Data were collected from four male subjects to determine the relationships between load, speed and muscle use during cycle ergometry. These data were then used to construct equations to govern the stimulation of muscle in paralysed individuals, during cycle ergometry induced by functional electrical stimulation (FES) of the quadriceps, gluteus maximus and hamstring muscles. The algorithm was tested on four subjects who were paralysed owing to a complete spinal cord injury between T4 and T11. Using the multivariate equation, the control of movement was improved, and work was accomplished that was double (2940 Nm min(-1) compared with 5880 Nm min(-1)) that of traditional FES cycle ergometry, when muscle stimulation was also controlled by electrical stimulation. Stress on the body, assessed by cardiac output, was increased almost two-fold during maximum work with the new algorithm (81 min(-1) compared with 15 l min(-1) with the new algorithm). These data support the concept that the limitation to workload that a person can achieve on FES cycle ergometry is in the control equations and not in the paralysed muscle.

Adult↗
PubMed2001

Microprocessor-based gait analysis system to retrain Trendelenburg gait.

A microprocessor-based gait analysis system is described that uses two electromyogram (EMG) amplifiers, two foot switches and an audio feedback device to allow the retraining of one type of improper gait, where the hip abductors (gluteus medius muscles) are weak on one side of the body, causing the opposite hip to drop during the swing phase of gait (Trendelenburg gait). As the abnormality is strictly on one side of the body in most people, the circuitry is minimised, as gait can be analysed by only comparing muscle activity in the affected gluteus medius muscle with that in the unaffected gluteus medius muscle, through the EMG. Two foot contact switches are used to help assess timing of the step cycle. If gait is different on the two sides of the body, an audio cue directs the patient to correct the abnormality by increasing activity on the affected side. The device is tested on five patients. Trendelenburg gait is reduced by an average of 29 degrees through the use of the device. The average stride length at the beginning of the study is 0.32 +/- 0.3 m. By the end of the study, the stride length is increased to 0.45 +/- 0.2 m for the entire group of five subjects. The speed of gait has increased from 1.6 +/- 0.4 kmh(-1) to 3.1 +/- 0.5km h(-1).

Adult↗
PubMed2001

The use of electromyogram biofeedback to reduce Trendelenburg gait.

Ten subjects suffering from incomplete spinal cord injuries, clinically diagnosed as walking with Trendelenburg gait, underwent a 2 month therapy program to strengthen their muscles and reduce their gait abnormalities. Therapy involved muscle strengthening and gait training for 2 h a day, 5 days a week in a clinic. Biofeedback was also accomplished for 30 min each training day on all subjects. In addition, five of the subjects wore a two-channel electromyogram (EMG) biofeedback training device at home to see if neuromuscular re-education outside of the clinical setting could speed their recovery. The difference for these five subjects was that they would have continuous biofeedback therapy every time they walked and not biofeedback limited to only 30 min a day. Since weakness of the gluteus medius muscles is the prime contributor to Trendelenburg gait, the device provided warning tones giving feedback of improper gait through bilateral assessment of the use of the gluteus medius muscles. If too little gluteus medius activity was seen on the affected side or the step was too short in duration, the microprocessor provided an audio cue to the subjects alerting them to correct the deficit. Subjects only undergoing clinical therapy showed about a 50% reduction in hip drop due to therapy. However, the group that used the home training device showed almost normal gait after the 2 month period.

Adult↗
PubMed2000

The relationship between exercise work intervals and duration of exercise on lower extremity training induced by electrical stimulation in humans with spinal cord injuries.

A group of 90 male paraplegics were studied to determine the optimal training protocol for isokinetic exercise induced by functional electrical stimulation of the quadriceps muscles. The parameters that were varied were the number of training sessions a week, the length of the training sessions each day, and the work-rest intervals in each training session. Training for 3 days a week for 30 min a day with 6 s of exercise and 6 s of rest proved the optimal protocol. Training for 5 days or for 1 day a week was not as effective in training strength or endurance. A combination of 50% work and 50% rest produced a much greater gain in strength and endurance than work:rest ratios of 66%:33% or 25%:75%. When training was conducted for 5 min, 15 min or 30 min each day, the greatest increase was found when the muscles were exercised for 30 min each day. While more variables need to be examined, this study has provided some initial guidelines for isokinetic training of humans using electrical stimulation.

Adult↗
PubMed2000

Blood pressure and heart rate responses during a fatiguing isometric exercise in paraplegic men with hypertension.

A group of 45 male subjects were examined in a cross-sectional study to compare the blood pressure response that occurs during isometric exercise maintained to fatigue among control subjects and paraplegic patients with (PH) and without essential hypertension (PN). Two muscle groups were examined: the handgrip muscles (voluntary effort) and the quadriceps muscles. The tension chosen for the contraction was 40% of the muscles maximum strength for both muscle groups. While the paraplegic groups had more strength in their handgrip muscles than that found for the controls, the control subjects had more strength in their quadriceps muscles than either of the paraplegic groups. During the fatiguing isometric contractions, the rate of rise and absolute systolic blood pressure was higher in the PH than the other groups of subjects. The diastolic pressure of the PH group, while elevated during exercise, was only elevated to the same degree as the increase in resting diastolic pressure above normal. Heart rate changes during exercise was the same in all groups of subjects for handgrip contractions. The controls had the same heart rate response to handgrip as to leg exercise. The paraplegic groups showed no heart rate change during fatiguing contractions of their quadriceps muscles. The PH group actually showed a reduction in heart rate during the leg exercise.

Blood Pressure↗
PubMed1992

The effect of training on endurance and the cardiovascular responses of individuals with paraplegia during dynamic exercise induced by functional electrical stimulation.

Endurance for dynamic exercise, cardiac output, blood pressure, heart rate, ventilation, and oxygen consumption was measured in eight individuals with paraplegia at the end of 4-min bouts of exercise on a friction braked cycle ergometer. Movement of the subjects' legs was induced by electrically stimulating the quadriceps, gluteus maximus and hamstring muscles with a computer-controlled biphasic square--wave current at a frequency of 30 Hz. The friction braked cycle ergometer was pedalled at work rates which varied between 0 and 40 W. Measurements were repeated after 3 and 6 months to assess the affect of training. After 3 months of training it was found that endurance increased from 8 min at a work rate of 0 W to 30 min at a work rate of 40 W. Compared to the cardiovascular responses in non-paralyzed subjects, computerized cycle ergometry was found to be associated with higher relative stresses for a given level of absolute work. Mean blood pressure, for example, increased by over 30% during maximal work in individuals with paralysis compared to the typical response obtained for able-bodied subjects. Analysis of the data showed that instead of the 20-30% metabolic efficiency commonly reported for cycle ergometry, the calculated metabolic efficiency during computer-controlled cycle ergometry was only 3.6%.

Adult↗
PubMed1992

Thermoregulatory stress during rest and exercise in heat in patients with a spinal cord injury.

Twelve subjects with spinal cord injuries and four controls (all male) were exposed to heat while sitting at rest or working at each of three environmental temperatures, 30, 35 and 40 degrees C, with a relative humidity of 50%. Exercise was accomplished at a load of 50 W on a friction-braked cycle ergometer which was armcranked or pedalled. Functional electrical stimulation of the legs was provided to the subjects with quadriplegia and paraplegia to allow them to pedal a cycle ergometer. The data showed that individuals with quadriplegia had the poorest tolerance for heat. As an example, in this group, accomplishing armcrank ergometry while working at an environmental temperature of 40 degrees C resulted in an increase in aural temperature of 2 degrees C in 30 min. The aural temperature of individuals with paraplegia working for the same length of time under the same conditions rose approximately 1 degree C. There was virtually no change in the aural temperature in the control subjects.

Adult↗
PubMed1991

Physiologic costs of computer-controlled walking in persons with paraplegia using a reciprocating-gait orthosis.

Blood pressure, heart rate, oxygen uptake, cardiac output, and the surface electromyogram from key muscle groups in the upper body were measured in four subjects with paraplegia during ambulation using only a reciprocating-gait orthosis (RGO) and using an RGO with movement assisted by functional electrical stimulation (FES) of the hamstring and gluteus maximus muscles. These data were compared to data collected on four able-bodied control subjects during ambulation at matched speeds. Whether walking with FES and RGOs or walking with RGOs alone, subjects had an optimum gait speed at which efficiency was highest. For paralyzed subjects using FES, the optimum walking speed was approximately 1.5 mph (2.4km/hr); without FES, the optimum speed averaged about 0.75mph (1.2km/hr). Blood pressure, heart rate, oxygen uptake, and cardiac output were measured during ambulation with FES and were found to be higher than those of controls, but they were significantly lower than those in the paralyzed subjects in RGOs with no FES. Electromyogram studies showed that the activity in upper body muscles was much higher when walking in RGOs without FES than in RGOs with FES.

Adult↗
PubMed1986

A computer model of neck muscle endurance and fatigue as a function of helmet loading.

A series of experiments were conducted in which the neck muscles of volunteer subjects were dynamically and statistically loaded by systematic variations of twenty-four headgear configurations consisting of eight different centers-of-gravity (CGs) times three different weights. Six subjects would rotate their heads laterally (from side-to-side) for 30 min with each of the headgear loading combinations. Immediately thereafter, the subject would position his head in an isometric head dynamometer and exert a sustained right lateral neck contraction or forward neck contraction at 70% of his maximum strength, during which endurance time (to fatigue) was recorded. The results indicate that the computer model makes reasonable predictions within the boundary conditions. Input data outside the boundary conditions is rejected. The assumption of insensitivity to vertical loading is demonstrated. The assumption of bilateral symmetric response was confirmed for the 1.45 kg and 2.27 kg helmet loads. However, this assumption was not confirmed for the 4.09 kg helmet load. It is concluded from the computer model that aftward, midline loading is the optimal CG location (i.e. maximal endurance) for heavier helmets in the 3-4 km range.

Adult↗
PubMed1985

Discharge characteristics of motor units and the surface EMG during fatiguing isometric contractions at submaximal tensions.

The RMS amplitude of the surface electromyogram (EMG) and the frequency of discharge of motor units was examined throughout the duration of isometric contractions of the adductor pollicis muscles sustained to fatigue at tensions of 25, 40, and 55% of the maximum voluntary strength (MVC) of eight male subjects during fatiguing isometric contractions. The maximum strength of the muscle and the EMG above the adductor pollicis muscles was also assessed during 3 s of voluntary and electrically induced isometric contractions interposed at 25, 50, 75, and 100% of the duration of the fatiguing contractions. At the point of fatigue from submaximal isometric contractions, the RMS amplitude of the surface EMG was highest for contractions at 55 as compared to 40 and 25% MVC. The lower RMS amplitude of the EMG during contractions at lower as compared to higher tensions at the point of fatigue was paralleled by a lower discharge frequency of the alpha motor neurons in the fatigued muscle during contractions at 25% as compared to 40 and 70% MVC. The reduction in discharge frequency was probably of a sufficient order of magnitude to account for the lower amplitude of the EMG at the end of fatiguing isometric contractions at lower tensions.

Aerospace Medicine↗
PubMed1985

Closed-loop control of movement of skeletal muscle.

Closed-loop (feedback) control of skeletal muscle is critically reviewed. The introductory section examines the advantages and disadvantages of open-loop as compared to closed-loop control in general, defines the problem, and outlines our approach. In the biological systems section, muscle structure and function are defined at the level of the motor nerve, neuromuscular junction, and sarcomere. Time delays, power and efficiency, fatigue, and other effects are also discussed in relation to the development of closed-loop control. This section then proceeds to review biological sensors and finally integrates this information by reviewing the body's own closed-loop control system. The third section critically reviews various approaches to the mathematical modeling of muscle. The control problem (in general) is reviewed with particular emphasis on contemporary control systems engineering. Essential to closed-loop control of paralyzed skeletal muscle is sensor technology. Therefore, the fourth section reviews external mechanical sensors. Specifically, potentiometers and Hall effect sensors, capacitive force transducers, inductive displacement transducers (LVDTs), and various position resolvers are discussed. Finally, the fifth section reviews the application of closed-loop control of skeletal muscle to the human being. The focus of this section is the paralyzed individual: past progress and future directions. An extensive bibliography of cited references is then provided so that the interested reader may pursue his/her particular area of interest in more detail. The authors acknowledge that such an extensive review of so many relevant areas is necessarily not complete and often overly simplistic, but our goal is a "first approach" to a comprehensive understanding of the closed-loop (feedback) control problem for achieving movement in paralyzed skeletal muscle.

Animals↗
PubMed1984

The interrelationship between blood pressure, intramuscular pressure, and isometric endurance in fast and slow twitch skeletal muscle in the cat.

Two series of experiments were performed to examine the interrelationships between blood pressure, intramuscular pressure, muscle blood flow, and the endurance for isometric exercise in a fast (medial gastrocnemius) and a slow (soleus) twitch muscle of the cat. In the first series of experiments, the relationship between tension and intramuscular pressure was examined. It was found that intramuscular pressure was linearly related to tension in both muscles. However, at any proportion of the muscles maximum tension, the intramuscular pressure of the medial gastrocnemius muscle (the stronger of the muscles) was about twice that of the soleus. A second series of experiments was conducted in which blood pressure was increased above intramuscular pressure and the effect of blood pressure on isometric endurance was measured. The pressure of the perfusing blood of the cat's hind limb was adjusted to either 13.3, 26.6, or 39.9 kPa. It was found that increased perfusion of the muscle resulted in a dramatic increase in the endurance for contractions sustained at isometric tensions below 60% of the muscle's initial strength. In contrast, for contractions above this tension, the effect of increased perfusion was much less pronounced.

Animals↗