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Biomedical subjects

R J Gregor

Publications and source records attributed to R J Gregor.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1984

Phasic relations in 90 degree abduction-adduction of the arm: the ARIMA representation.

Myoelectric signals (MES's) from the medial deltoid, posterior deltoid and medial trapezius were analyzed during 90 degree abduction-adduction cycles of arm movement. Two healthy males were utilized as subjects. The MES's records were divided into sub-sections of 50 ms of duration, and each segment was described by a suitable model. The models were based on autoregressive integrated moving average (ARIMA) processes. Several distinct phases were discerned within a given movement cycle, each phase being associated with a distinct type of ARIMA process. Phasic relations among the three muscles were then revealed. A simple test was suggested to detect the onset of muscle activity in real-time situations.

Arm↗
PubMed1984

A technique for estimating mechanical work of individual muscles in the cat during treadmill locomotion.

Mechanical work, the product of force and length change, was assessed in selected hindlimb extensors of two adult cats during three different speeds of unrestrained treadmill locomotion. Forces were measured using implanted transducers placed on the soleus (SOL) and medial gastrocnemius (MG) tendons. A three dimensional technique of muscle length estimation using high speed cinematography was found preferable to either two dimensional or trigonometric measurements derived from anatomical and kinematic parameters. Length excursions increased in both muscles as treadmill speed increased. However, at all speeds of locomotion, the uniarticular SOL exhibited a greater range of motion than the biarticular MG. Increases in treadmill speed resulted in higher peak forces in the MG and constant or slightly lower peak forces in the SOL. These speed-dependent changes in length and force resulted in higher total positive work, lower total negative work, and higher net work for both muscles with increasing speeds. These data illustrate the importance of three-dimensional kinematics in determining changes in muscle length and describe the relative force and work changes in a slow and fast ankle extensor with changes in speed of locomotion.

Animals↗
PubMed1983

Responses of elbow extensors to landing forces during jump downs in cats.

Forces and displacements at the elbow joint have been related to EMG responses of flexor and extensor muscles during landing from jump downs at heights of 1.2 m to 0.6 m in five cats. Prelanding EMG activity consisted of two prelanding extensor bursts. Onset of both bursts was constant across all jump heights with reference to landing and not to take-off, occurring on average 73 +/- 12 ms and 17 +/- 8 ms prior to ground contact for the lateral triceps. Post-landing EMG activity was less than prelanding activity and was often packaged in three bursts, occurring on average at 18 +/- 6, 34 +/- 8 and 50 +/- 9 ms after touchdown. Other measurements from extensor EMG including burst duration and integrated activity pre- and post-landing were also invariant. Across jump heights, maximum flexion angular velocity and elbow displacement were reached on average 28 +/- 5 and 85 +/- 7 ms postlanding, respectively. Although vertical (y) and horizontal (x) ground reaction forces increased with jump height, torque values at the elbow joint were not significantly different and were small in magnitude. At landing an animal typically experienced a 20 ms flexor torque (0.3 Nm/kg b.wt.) followed by an extensor torque (0.4 Nm/kg b.wt.) that continued for the major portion of elbow flexion. The temporal constancy of the kinematic and kinetic data and EMG activity across jump heights suggests that a generalized motor program can be used to activate extensor muscles at the elbow joint during the prelanding phase of self-initiated jumps. Since the onset of extensor activity is related to landing rather than to take-off, it is hypothesized that this activity is triggered by visual cues rather than by vestibular reflexes. After impact, adjustments for slight differences in post-landing torque about the elbow may be accomplished by intrinsic properties of the activated muscle as well as through segmental reflexes.

Animals↗
PubMed1983

Correlation of myoelectric activity and muscle force during selected cat treadmill locomotion.

The purpose of this investigation was to associate the force produced by the cat medial gastrocnemius (MG) during unrestrained treadmill locomotion with the corresponding myoelectric signals (MES's). An intervention analysis based on the autoregressive-integrated moving average (ARIMA) process was performed on records obtained at treadmill speeds of 0.67 ms-1 and 2.24 ms-1. Results indicate that the pattern of MG myoelectric activity during a single step cycle may be divided into two parts. The primary burst (E1 burst) of activity occurs before foot contact and represents an energy build up which is related to a major part of the MG force monitored at the tendon. During stance, a second burst of activity is depicted by an almost critically damped second order system, and is responsible for the residual tension observed. Thus in vivo forces can be linked to MES's provided that phase differences between electrical and mechanical responses are taken into account.

Animals↗
PubMed1981

Skeletal muscle properties and performance in elite female track athletes.

Selected biochemical and physiological properties of skeletal muscle were studied in light of performance capabilities in 24 elite female track athletes. The feasibility of quantifying end point histochemistry and relating oxidative staining density (reduced nicotinomide adenine dinucleotide diaphorase: NADH-D) to whole body maximal oxygen consumption (VO2 max) was also investigated, while muscle fiber types, classified according to alkaline APTase stains, were studied and related to muscle oxidative capacity (succinate dehydrogenase: SDH), VO2 max and "in vivo" torque-velocity properties. Muscle biopsies were taken from the vastus lateralis of each subject and maximal knee extensor torques were recorded at 30 degrees from full extension at four selected velocities. While results confirm earlier reports on skeletal muscle properties and performance it was concluded that end point histochemistry could be reliably quantified and that an "oxidative" stain such as NADH-D correlates extremely well with VO2 max (r = 0.86, p less than 0.001) whereas correlations between % slow twitch fibres (Alkaline ATPase stain) and VO2 max were lower (r = 0.44, p less than 0.05). Additionally, as knee extension velocity increased from 0-1.7 rad x s-1 angle specific extensor torque production did not decline as observed in vitro and pentathletes displayed significantly larger torques at all velocities when compared to the other athletes. These data confirm that while myofibrillar ATPase staining correlates with force-velocity properties of muscle, VO2 max is better correlated with quantified oxidative staining.

Adenosine Triphosphatases↗
PubMed1981

Evidence for generalized motor programs using gait pattern analysis.

Human intra limb gait kinematics were analyzed via statistical and structural pattern recognition methods to determine the role of relative timing of limb segments within and between modes of gait. Five experienced runners were filmed while walking (3-6 km/hour) and running (8-12 km/hour) on a motor driven treadmill. Kinematic data consisted of relative timing of the four phases of the Philippson step cycle and intersegmental limb trajectories, determined from angle-angle diagrams. Despite marked decreases in absolute time durations within gaits remained constant over the speeds which were studied. Although a 2-fold increase in locomotor speed occurred in walking and a 1.5-fold speed increase occurred within running, the percentage of time spent in each of the Philippson phases was not significantly changed. However, significant differences in the time percentages and sequences of the step cycle phases were found between walking and running. Correlations between limb segment trajectories occurring in the different gaits showed strong coherence for overall step cycle patterns, but within step cycle phases and across speeds, selective phases displayed little correspondence.

Journal Article↗
PubMed1980

Kinetic and kinematic factors involved in the execution of front aerial somersaults.

The purpose of this investigation was to study the variation in ground reaction forces during take-off and to calculate the angular impulse produced about the center of mass by these forces during execution of a front aerial somersault. Additionally, several kinematic variables were discussed in relation to performance. Nine high level female gymnasts volunteered as subjects. Ground reaction force (GRF) patterns were monitored by a Kistler force platform and the selected kinematic variables were calculated from high speed film synchronized with the force records. Total body center of mass position was determined and subsequently used in the calculation of angular impulse during rear, double, and front leg support. While results showed similar angular impulse patterns across our subject population, a variety of kinetic and kinematic variables were presented in order to more completely discuss the components of angular impulse development during the take-off phase of a front aerial somersault. For example, while the mean angular impulse was 61.7 Nms (+/- 13.1), a surprising finding was the contribution made to this impulse by the rear leg, 70.9% (+/- 7.2).

Adolescent↗
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↗