Biomedical subjects

J Cholewicki

Publications and source records attributed to J Cholewicki.

43 records · Page 3Linked to original sources

PubMed1995

Relationship between muscle force and stiffness in the whole mammalian muscle: a simulation study.

Several types of analyses in biomechanics require estimates of both muscle force and stiffness. Simulations were performed using the two-state cross-bridge Bond Distribution-Moment muscle model of Zahalak (1981), together with other parameters for passive elasticity and tendon compliance, to estimate instantaneous stiffness and to compare these estimates with the wide range of values reported in the literature. While the relatively simple cross-bridge theory appears to approximate the stiffness of skinned muscle fibers, the stiffness of a complete muscle-tendon unit become complex and non-linear due to relative changes in muscle-tendon length and interaction with activation and length dependent passive elastic components. It would appear that the variability in muscle stiffness values reported in the literature can be explained with the D-M approach.

Biomechanical Phenomena↗

PubMed1994

EMG assisted optimization: a hybrid approach for estimating muscle forces in an indeterminate biomechanical model.

There are two basic approaches to estimate individual muscle forces acting on a joint, given the indeterminacy of moment balance equations: optimization and electromyography (EMG) assisted. Each approach is characterized by unique advantages and liabilities. With this in mind, a new hybrid method which combines the advantages of both of these traditional approaches, termed 'EMG assisted optimization' (EMGAO), was described. In this method, minimal adjustments are applied to the individual muscle forces estimated from EMG, so that all moment equilibrium equations are satisfied in three dimensions. The result is the best possible match between physiologically observed muscle activation patterns and the predicted forces, while satisfying the moment constraints about all three joint axes. Several forms of the objective function are discussed and their effect on individual muscle adjustments is illustrated in a simple two-dimensional example.

Algorithms↗

PubMed1992

Lumbar posterior ligament involvement during extremely heavy lifts estimated from fluoroscopic measurements.

The mechanical role of the lumbar posterior ligaments during lifting tasks remains controversial. This study was designed to assess the ligament and disc contribution in resisting trunk flexion moment during extremely heavy lifts performed by national class powerlifters. Direct measurements of lumbar vertebrae kinematics in sagittal plane were obtained from videofluoroscopy utilizing multiple digitizing, correction for optical distortions and digital filtering. Four experienced powerlifters executed three trials, resulting in about 72 mA s of total radiation exposure. In the first trial, joint angles were measured when subjects fully flexed their spines to a point where the passive tissues resisted the flexor moment creating myoelectric silence in the extensor musculature. Next, two conventional deadlift style lifts were executed with the barbell load ranging from 183.7 to 210.9 kg. Four vertebral corners were digitized at a sampling rate of 30 Hz. The relative intervertebral joint angles, distance between the ligament attachment points, shearing and compressive displacements were calculated from a rigid body motion approach. Analysis revealed that except for one trial of one subject, they accomplished their lifts with an amount of lumbar flexion between 1.5 and 13 degrees less than they demonstrated during full flexion. Resultant ligament lengths at the beginning of the lifts ranged from 56.1 to 99.8% of their lengths when the trunk was fully flexed. It was concluded that ligaments did not strain sufficiently to contribute substantial resistance to the trunk flexion moment, relegating this responsibility to the musculature.

Adult↗

PubMed1991

Lumbar spine loads during the lifting of extremely heavy weights.

The reaction moments at the knee, hip, and L4/L5 joints, and the compressive and shearing forces on L4/L5 are documented in powerlifters competing in a national powerlifting championship. Analyses were made of 13 female and 44 male competitors. The joint moments and forces were estimated from a linked segment model (WATBAK) that incorporated functional low back extensor musculature with a moment arm of 6 cm and a line action that was oriented 5 degrees posteriorly to the L4/L5 compression axis. This oblique orientation of the extensor muscles reduced the anterior shearing load on the vertebral motion unit. Average compressive loads on L4/L5 were estimated up to 17,192 N while the highest average L4/L5 and hip moments were 988 and 1047 N.m, respectively. The sumo deadlift style resulted in a 10% reduction in the joint moment and 8% reduction in the load shear force at the L4/L5 level when compared with the conventional lifting style. Formulation of linear regression equations to predict the load lifted using reaction joint moments yielded substantial unexplained variability, though significant relationships were found. This analysis suggested that there is large variability in the pattern of loading joints among national class powerlifters.

Biomechanical Phenomena↗

PubMedDate not supplied

A history of low back injury is a risk factor for recurrent back injuries in varsity athletes.

In this prospective study, we investigated whether a history of previous low back injury and dissatisfaction with a coach and teammates could predict future low back injury in varsity athletes during a 1-year follow-up period. Of 679 Yale varsity athletes surveyed in 1999, 18.3% (124) reported that they had sustained a low back injury within the past 5 years, and 6.8% (46) sustained a low back injury in the follow-up season. There were no differences in incidence rates between men and women or between athletes involved in contact or noncontact sports. A history of low back injury was the significant predictor for sustaining low back injury in the following year, and athletes who reported previous low back injury were at three times greater risk. Athletes who still had pain at the time of the survey were six times more likely to sustain a low back injury than were athletes without a history of low back injury. These results suggest that some risk factors associated with a history of low back injury predispose athletes to sustain recurrent injury. They may be congenital or a result of insufficient recovery time after the first low back injury episode.

Adult↗

PubMedDate not supplied

The effect of anabolic steroids and corticosteroids on healing of muscle contusion injury.

The effect of an anabolic steroid (nandrolone decanoate, 20 mg/kg) and a corticosteroid (methylprednisolone acetate, 25 mg/kg) on healing muscle injured with a drop-mass technique in a reproducible muscle contusion injury model in the rat was studied. Healing was determined by measuring active contractile tension in each muscle and histologic analysis. At day 2, the corticosteroid group showed significant improvement in both twitch and tetanic strength relative to the controls. At day 7, this effect was reversed and the corticosteroid muscles were significantly weaker than the control muscles, but there was still no significant effect seen in the anabolic steroid group. At day 14, the corticosteroid muscles were totally degenerated, with disorganized muscle fiber architecture. The anabolic steroid muscles were significantly stronger in twitch, and a similar trend was seen in tetanus relative to control muscles. The results indicate that in an animal model corticosteroids may be beneficial in the short term, but they cause irreversible damage to healing muscle in the long term, including disordered fiber structure and a marked diminution in force-generating capacity. Anabolic steroids may aid in the healing of muscle contusion injury to speed the recovery of force-generating capacity. Although anabolic steroids are considered renegade drugs, they may have an ethical clinical application to aid healing in severe muscle contusion injury, and their use in the treatment of muscle injuries warrants further research.

Anabolic Agents↗

PubMedDate not supplied

Are adolescent idiopathic scoliosis and ankylosing spondylitis counter-opposing conditions? A hypothesis on biomechanical contributions predisposing to these spinal disorders.

Human spinal biomechanics are profoundly complex and not well understood, especially in terms of the dynamic spine function. Translation of biomechanics to disease is difficult, particularly since cause must be separated from effect. Primary dynamics predisposing to the onset of chronic spinal disorders, e.g., adolescent idiopathic scoliosis (AIS) or ankylosing spondylitis (AS), must clearly be differentiated from secondary alterations. This commentary addresses primary biomechanics that may predispose to these idiopathic diseases. A novel hypothesis is proposed, based upon inferences regarding their contrasting muscular dynamics. The hypothesis postulates opposing inherent muscle tonicity in AIS versus AS. Converse degrees of spinal stability may predispose to the respective curvature deformities of AIS and the enthesopathy lesions of AS. One condition is suspected to counter-oppose the other, within a polymorphic spectrum of spinal stability.

Adolescent↗