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Biomedical subjects

R J Gregor

Publications and source records attributed to R J Gregor.

At least 19 recordsLinked to original sources
PubMed1992

Biomechanics of sprint running. A review.

Understanding of biomechanical factors in sprint running is useful because of their critical value to performance. Some variables measured in distance running are also important in sprint running. Significant factors include: reaction time, technique, electromyographic (EMG) activity, force production, neural factors and muscle structure. Although various methodologies have been used, results are clear and conclusions can be made. The reaction time of good athletes is short, but it does not correlate with performance levels. Sprint technique has been well analysed during acceleration, constant velocity and deceleration of the velocity curve. At the beginning of the sprint run, it is important to produce great force/power and generate high velocity in the block and acceleration phases. During the constant-speed phase, the events immediately before and during the braking phase are important in increasing explosive force/power and efficiency of movement in the propulsion phase. There are no research results available regarding force production in the sprint-deceleration phase. The EMG activity pattern of the main sprint muscles is described in the literature, but there is a need for research with highly skilled sprinters to better understand the simultaneous operation of many muscles. Skeletal muscle fibre characteristics are related to the selection of talent and the training-induced effects in sprint running. Efficient sprint running requires an optimal combination between the examined biomechanical variables and external factors such as footwear, ground and air resistance. Further research work is needed especially in the area of nervous system, muscles and force and power production during sprint running. Combining these with the measurements of sprinting economy and efficiency more knowledge can be achieved in the near future.

Acceleration↗
PubMed1991

A comparison of the triceps surae and residual muscle moments at the ankle during cycling.

The rigid linked system model and principles of inverse dynamics have been widely used to calculate residual muscle moments during various activities. EMG driven models and optimization algorithms have also been presented in the literature in efforts to estimate skeletal muscle forces and evaluate their possible contribution to the residual muscle moment. Additionally, skeletal muscle-tendon forces have been measured, directly, in both animals and humans. The purpose of this investigation was to calculate the moment produced by the triceps surae muscles and compare it to the residual muscle moment at the ankle during cycling at three power outputs (90, 180 and 270 W). Inferences were made regarding the potential contribution made by each triceps surae component to the tendon force using EMG and muscle-tendon length changes. A buckle-type transducer was surgically implanted on the right Achilles tendon of one male subject. Achilles tendon forces measured in vivo were multiplied by their corresponding moment arms to yield the triceps surae moment during the three working conditions. Moment arm lengths were obtained in a separate experiment using magnetic resonance imaging (MRI). Pedal reaction forces, body segment accelerations (determined from high speed film), and appropriate mass parameters served as input to the inverse solution. The triceps surae moment was temporally in phase with and consistently represented approximately 65% of the residual muscle moment at the ankle. These data demonstrate the feasibility of using implanted transducers in human subjects and provide a greater understanding of musculoskeletal mechanics during normal human movements.

Achilles Tendon↗
PubMed1990

Weight-bearing hindlimb stepping in treadmill-exercised adult spinal cats.

Hindlimb locomotion on a motor-driven treadmill was studied in 5 cats spinalized at a low thoracic level adults. Six months after surgery, the cats were anesthetized and implanted for electromyographic (EMG) and force recordings in hindlimb muscles. For the last 5 months of the spinalization period, the hindlimbs of each cat were exercised daily for 30 minutes on a treadmill. Data were collected during hindlimb locomotion on a treadmill across the entire range of speeds each cat could accommodate. All trials were filmed (100 frames/s) for kinematic analysis. EMG data were recorded from the soleus (Sol), medial gastrocnemius (MG), tibialis anterior (TA) and extensor digitorum longus (EDL). Forces were recorded in vivo from the Sol and MG tendons. All cats could sustain full weight-bearing stepping without the need for mechanical stimulation of the tail. Although the general stepping pattern of the spinal cats was remarkably similar to that of normal cats, several key differences were identified. Compared to normal cats, the adult spinal cats walked at a lower range of speeds and exhibited a longer swing phase duration. The Sol produced forces and displayed activation periods comparable to those observed in normal cats. The MG of adult spinal cats, however, produced lower forces and had a later onset of activation in comparison to normal cats. Each of the muscles in all spinal cats exhibited tremor during stepping. These results suggest that there were limitations in the activation levels of some hindlimb flexor and extensor muscles during treadmill locomotion. These data further suggest that, in normal cats, accommodation to treadmill speed is accomplished by modulating supraspinal input to the lumbar spinal cord while leaving many of the timing details to be regulated by lumbar spinal networks.

Animals↗
PubMed1990

In vivo moment arm calculations at the ankle using magnetic resonance imaging (MRI).

In vivo moment arm lengths for the Achilles tendon and tibialis anterior (TA) were determined in 10 adult male subjects. Moment arms were measured as the perpendicular distance between the joint center of rotation (CR) and the center of the muscle's tendon on a series of sagittal plane magnetic resonance images. The first set of calculations used a fixed CR and the second a moving CR. The position of the CR was determined using a modification of the graphical method of Reuleaux. For both moving and fixed CR conditions, moment arms increased by approximately 20% for the Achilles tendon and decreased by approximately 30% for the TA when the ankle moved from maximum dorsiflexion to maximum plantarflexion. Moment arms averaged 3.1% greater for the Achilles tendon and 2.5% greater for the TA when calculated using a fixed CR. These data suggest that the averaged moment arm lengths for the Achilles tendon and the TA were relatively unaffected by the use of a fixed vs moving CR.

Achilles Tendon↗
PubMed1989

Electromyographic activity of cat hindlimb flexors and extensors during locomotion at varying speeds and inclines.

Electromyographic activity (EMG) was used to determine how hindlimb muscle activation patterns are modified as speed and incline of locomotion are varied in treadmill-trained cats. EMG was recorded using chronically implanted i.m. electrodes from the soleus, medial gastrocnemius, gluteus medius, and tibialis anterior muscles of adult cats during treadmill locomotion at a range of speeds and inclines. The patterns of changes in EMG activity at varying speeds and inclines were similar in all cats. Across speeds, the integrated EMG per step decreased for the soleus but remained constant for the other muscles. The integrated EMG per step was elevated in all muscles at higher inclines. Generally, with increased speed or incline the mean EMG per step was elevated in the medial gastrocnemius, gluteus medius, and tibialis anterior, the largest increase seen in the medial gastrocnemius. Soleus mean EMG per step remained unchanged with increased speed, but showed an absolute increase at the higher inclines. The integrated EMG per minute was always highest for the soleus followed by the medial gastrocnemius, and always lowest for the tibialis anterior. At the faster speeds, the 'on-time' increased in the tibialis anterior and decreased in the other muscles. These data suggest that the number of motor units activated and/or their firing frequencies increased in the medial gastrocnemius and the gluteus medius during locomotion at faster speeds or larger inclines, while relatively little change occurred in the soleus and tibialis anterior. These data also suggest that while there is considerable modulation of the level and duration of excitation of the extensor motor pools there is relatively little modulation of the flexor motor pools to adjust for both the speed and the incline of locomotion.

Acceleration↗
PubMed1989

Endogenous Nocardia asteroides subretinal abscess diagnosed by transvitreal fine-needle aspiration biopsy.

The authors report a case of an endogenous Nocardia asteroides subretinal abscess in an immunosuppressed cardiac transplant recipient. On clinical grounds, the metastatic subretinal abscess was initially thought to be a fungal, atypical bacterial, or viral lesion. Transvitreal fine-needle aspiration biopsy of the lesion yielded a sufficient specimen for immediate preliminary identification of the microorganism and permitted prompt initiation of an appropriate antibiotic regimen. The definitive diagnosis was based on culture of the organism from the needle aspirate.

Abscess↗
PubMed1989

Spontaneous regression of choroidal melanoma over 8 years.

The authors observed clinical regression of an apparent primary choroidal melanoma in a 66-year old man over an eight-year interval. This regression was documented photographically and ultrasonographically. The authors discuss the possible mechanisms responsible for this clinical course.

Aged↗
PubMed1988

Differential kinetics of fast and slow ankle extensors during the paw-shake in the cat.

Force, length, and EMG were assessed in the medial gastrocnemius and soleus muscles of two cats during the paw-shake response. The medial gastrocnemius produced high forces and significant electrical activity while force production and electrical activity were negligible in the soleus. This observation is significant as it provides evidence, through the direct measurement of muscle force, of selective recruitment of a fast muscle when a slow synergist is not activated. Additionally, the relationship among force, length, and neural activation indicates that the role of the medial gastrocnemius during the paw-shake response is to decelerate muscle lengthening and begin muscle shortening.

Animals↗
PubMed1988

Mechanical output of the cat soleus during treadmill locomotion: in vivo vs in situ characteristics.

To study the mechanical output of skeletal muscle, four adult cats were trained to run on a treadmill and then implanted under sterile conditions and anesthesia with a force transducer on the soleus tendon and EMG electrodes in the muscle belly. After a two-week recovery period, five consecutive step cycles were filmed at treadmill speeds of 0.8, 1.3 and 2.2 m s-1. Locomotion data in vivo included individual muscle force, length and velocity changes and EMG during each step cycle. Data for an average step cycle at each speed were compared to the force-velocity properties obtained on the same muscle under maximal nerve stimulation and isotonic loading conditions in situ. Results indicate that the force and power generated at a given velocity of shortening during late stance in vivo were greater at the higher speeds of locomotion than the force and power generated at the same shortening velocity in situ. Strain energy stored in the muscle-tendon unit during the yield phase in early stance is felt to be a major contributor to the muscle's enhanced mechanical output during muscle shortening in late stance.

Animals↗
PubMed1988

The muscle activity paradox during circular rhythmic leg movements.

A cyclist's legs make a simple 360 degrees circular and rhythmic movement, activated by a simple flexion-extension function in a sagittal plane. However, because of the simultaneous combination of leg rotation in the hip, knee and ankle joint with translation of the upper body, the general motion becomes quite complex. This complexity is increased by the anatomical interpretations of EMG readings taken during the pedalling cycle, indicating a high activity of 'flexor' muscles during the downward 'extension' of the leg (0-90 degrees propulsion phase of the pedalling cycle). This calls for an anatomical paradox. In order to verify these interpretations, the activity of six lower limb muscles was measured under field circumstances on nine elite cyclists using a portable EMG data acquisition system and active surface electrodes allowing remote (non-telemetric) monitoring of the cyclists' muscle activity patterns. Measurements were made during a 1000 m submaximal but constant effort and during a 200 m sprint. Confirmation of the anatomical paradox was found in both test circumstances. Analyses of the normalized EMG in combination with torque values of both hip and knee during the pedalling cycle indicate a zero torque at 135 degrees for the knee, while at this same angle the overall extensor activity ends in one leg and starts simultaneously in the other leg (at 315 degrees). Since the propulsion does not continue until 180 degrees, the flexor muscles have to be activated before the extension activity ends in order to generate the continuation of the circular motion until (and beyond) the bottom dead centre (180 degrees).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Achilles tendon forces during cycling.

Cycling represents an activity, in which the leg extensor muscles have been thought to contract only concentrically. In the present investigation, the forces of the triceps surae muscles were recorded directly in vivo from the achilles tendon (AT) of a healthy male subject, who pedaled on the standard bicycle ergometer at varying work loads (88, 176, and 265 W). EMGs from the vastus medialis (VM), gastrocnemius (GAST), soleus (SOL), and tibialis anterior (TA) muscles were recorded telemetrically together with the AT force. Muscle length changes during the complete pedaling cycles were estimated from the film analysis. The results indicated that the peak AT forces increased from 489 N at 1 kp (90 rpm) to 661 N at 3 kp (90 rpm). This peak force, which was recorded at 115 degrees of the pedaling cycle, did not change with increase in the pedaling cadence. While SOL muscle did not demonstrate any increase in length during the power phase of the cycle, the GAST experienced an increase in length between 0 and 90 degrees of the pedaling cycle, and the total increase was 2.5% of the segment length. VM and SOL muscles demonstrated the greatest activity during the early power phase and remained almost quiescent during the latter part of the cycle. TA activation began simultaneously with the cessation of VM and SOL activity. GAST obtained its peak EMG activity at 104 degrees at a point when it was still lengthening. The results can be interpreted to indicate an existence of a stretch-shortening cycle, especially for the GAST muscles, during the active phase of the pedaling cycle.(ABSTRACT TRUNCATED AT 250 WORDS)

Achilles Tendon↗
PubMed1986

Effects of training on the recovery of full-weight-bearing stepping in the adult spinal cat.

The effects of ambulatory training on the extent and time course of recovery of weight-bearing-stepping in cats spinalized (T12-T13) as adults were investigated. One month after spinal cord transection, 14 of 16 cats were capable of bearing the full weight of their hindquarters with their hind limbs during stepping on a motor-driven treadmill if the tail was pinched or crimped. Of those 14 cats 8 were assigned to a trained and 6 to an untrained group. Trained cats were subjected to 30 min/day of treadmill exercise, 5 days/week. Training was initiated 1 month posttransection and continued until 5 to 7 months posttransection. Daily records were kept on the treadmill speeds used, the time at each speed, and the number of steps that were not full weight bearing. The number of full-weight-bearing steps times treadmill speed was used as a measure of performance. The tail was crimped whenever necessary, but was required less and less as training progressed. Performance plateaus were reached between 25 and 85 days after initiating training (mean = 48 +/- 22 days). Maximum treadmill speeds increased in untrained cats from 0.075 +/- 0.042 m/s 1 month posttransection to 0.240 +/- 0.042 m/s 5 to 7 months posttransection and those of trained cats increased from 0.079 +/- 0.045 m/s to 0.619 +/- 0.133 m/s during this same period. We conclude that a much larger proportion of adult spinal cats are capable of full-weight-bearing stepping than reported, and that training which emphasizes early tail crimping and complete weight bearing at all times results in marked improvements in the locomotor capacity of the hind limbs.

Animals↗
PubMed1985

Knee flexor moments during propulsion in cycling--a creative solution to Lombard's Paradox.

The function of two joint muscles in the human lower extremity was studied during a cycling task with efficiency of their action discussed in light of Lombard's Paradox. Special pedals were designed to monitor reaction forces parallel to the sagittal plane of the body. Net moments of force about the hip, knee and ankle and EMG patterns in selected lower extremity muscles were recorded in five subjects pedalling against a constant load. The most original aspect of this study was the clear difference in hip and knee action during the propulsive phase of the pedalling cycle. A knee flexor moment was consistently observed in all subjects starting approximately half way through the propulsive phase of crank rotation (0-180 degrees) and presented as a creative solution to Lombard's Paradox.

Bicycling↗
PubMed1979

Torque-velocity relationships and muscle fiber composition in elite female athletes.

The relationship between the predominance of fast and slow muscle fibers of the vastus lateralis and "in vivo" torque velocity properties in 22 female athletes was studied. Fiber types were classified according to the histochemical myofibrillar adenosine triphosphatase technique at a basic pH. Maximal extensor troques were recorded at 30 degrees from full extension at four selected velocities. While results confirm earlier reports on muscle fiber type and performance, an additional finding was that as knee extension velocities increased from 0 to 95 degrees/s angle specific extensor torque production did not decline as seen in in vitro muscle preparations. The difference in extensor torque between 0 and 96 degrees/s appeared far more critical than the differences observed between 96 and 288 degrees/s. Significant differences in torque were seen at 96, 192, and 288 degrees/s in thos with greater than 50% and less than 50% slow-twitch fibers. When expressed per kilogram of body weight the subjects with greater than 50% fast-twitch fiber produced the greatest torque at 192 degrees/s. These results suggest that the velocity at which torque begins to decline in vivo is related to the proportion of slow-twitch fibers in the vastus lateralismuscle.

Adolescent↗