Relationship of isometric and isokinetic torques

4.88

Abstracts

When immature whole bone is bent beyond the elastic limit it exhibits non-elastic yielding and permanent deformation without concomitant boney fracture. Mature bone is stiffer, has a substantially decreased amount of non-elastic deformation and does not exhibit permanent angulation after load release. In order to investigate age-related changes paired remora and tibia were obtained from 22 labradors ranging in age from one week to adult. Three and four point bending tests were performed to determine each bone’s stiffness, yield strength, maximum bending moment and total amount of permanent deformation after load release. Bending tests showed that all bones exhibited an initial linear region followed by a large region of non-elastic deformation. Stiffness increased with maturity while non-linear deformation decreased substantially. In the youngest bones large permanent deformations were noted upon load release, with decreasing amounts of permanent deformation occurring with maturity. In all bones the structural rigidity increased with age, indicating a greater ability to carry load. AGE AND SEX DIFFERENCES

IN GEOMETRICAL

PROPERTIES

OF THE HUMAN FEMUR AND TIBIA

and W. C. HAYES (Orthopaedic Biomechanics Laboratory, Beth Israel Hospital and Harvard Medical School, 330 Brookline Avenue, Boston, MA)

C. B. RIJFF

Using a digitizer and interactive computer software, section properties (areas. centroids, principal moments and their orientations) were determined at 11 femoral and tibia1 cross-section locations in 120 individuals obtained from an osteological collection. Significant differences in geometrical properties were observed between males and females and between age groups. Endosteal resorption with aging was found to be largely offset by subpet-iosteal expansion in both sexes, although females showed a net loss (10%) in cortical area. Some sexspecific changes with age in relative magnitude and orientation of the principal moments were also observed which appeared to be related to patterns of bone loss in the femoral and tibia1 diaphyses and to changes in the orientation of the femoral neck with aging. Thus, changes in long bone cross-sectional geometries appear to compensate for sex and age-related patterns of bone loss. D. MUSCLE STRENGTH

RELATIONSHIP

OF ISOMETRIC

AND ISOKlNETlC

TORQUES

for Special Surgery, 535 East 70th Street, New York, NY)

JAMES C. OTIS (Department

of Biomechanics,

Hospital

Isokinetic muscle testing has become an increasingly popular method for measuring muscle performance. However, the significance of the dyamic strength measurements obtained remains unclear, particularly with respect to the relationship of isometric to isokinetic measurements. The relationships between maximal isometric and maximal isokinetic torques were investigated at angular velocities of 12’/sec and 24”/sec for both flexion and extension of the elbow joint. Thirty males and females were tested bilaterally and torques were obtained at the 60’ and 90” positions. Linear and nonlinear regressions of isometric vs isokinetic torque yielded correlation coefficients averaging 0.93 and 0.95, respectively. The results demonstrated a strong correlation between static and dynamic strength for the velocities used and also demonstrated the existence of a nonlinear frictional component related to muscle strength. MECHANICAL

RATIOS OF SELECTED

BODY LEVERS AS THEY RELATE TO THE PERCEST

SLOW

TWITCH/FAST TWITCH MUSCLE FIBERS INvOL\‘ED BLAUER L. BANGERTER (Department

of Physical

Education,

Brigham

Young University,

Provo, UT) The mechanical ratios of body levers moved by 8 selected muscles (soleus. tibialis anterior, deltoid, biceps, gastrocnemius, vastus lateralis, rectus femoris and triceps) were measured on 5 cadavers. These ratios were correlated with percent slow twitch tibres (STF) for the corresponding muscle biopsies from nine subjects (reported in a study by Saltin et al., 1977 Annals New York Academy of Science. 301, 3-29, citing data from Johnson et al., 1973, Nygaard er al., 1976 and Costill et al., 1976). The resulting ‘r’ was 0.860. The muscles listed above were in descending order of percent ST fibres, the soleus showed 88% STF, and the triceps 33% STF with respective mechanical ratios of 2.6: 1 and 0.1: 1. The Costill study of 14 elite distance (marathon) runners exhibited 79% STF in the gastrocnemius which in the running action also had a mechanical ratio of 2.6: 1. Structure and function appeared to meet expected relationships. STRENGTH JAMES

TRAINING:

G.

Laboratory,

THE EFFECTS

HAY, JAMES

Department

G.

OF LOAD AND RATE OF EXERCISE OS JOINT KINETICS

ANDREWS

of Physical

and

CHRISTOPHER

Education.

L. VACGHAN (Biomechanics

University

of Iowa,

Iowa City,

IA)