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Biomedical subjects

R M Alexander

Publications and source records attributed to R M Alexander.

At least 55 records · Page 3Linked to original sources
PubMed1985

The maximum forces exerted by animals.

This paper reviews the maximum forces exerted by animals in a wide range of activities including running, jumping, swimming and biting. Most of the data refer to vertebrates and arthropods, ranging in size from 0.5-mg fleas to 3-tonne elephants. Maximum forces exerted on the environment give values of (force/body weight) which lie, in most cases, between 0.5 body mass-1/3 (kg) and 20 body mass-1/3. Maximum forces exerted by major muscle groups give values of (force/body weight) in most cases between 10 body mass-1/3 and 50 body mass-1/3.

Animals↗
PubMed1984

Optimum strengths for bones liable to fatigue and accidental fracture.

Limb bones are liable to fail by fatigue, due to stresses imposed repeatedly in activities such as running. They may also be broken by larger stresses which occur occasionally in accidents. Too weak a bone will probably fail but too strong a bone is unduly heavy. A mathematical model predicts optimum strengths for bones subject to the hazards both of fatigue and of accidents. When accidents are mild and predictable, fatigue is the more important hazard. When they are large and unpredictable they are the more important hazard and stronger bones are generally preferred, but in extreme cases it may become advantageous to dispense with the bone. There is a restricted range of circumstances in which fatigue and accidents are both important hazards. The strengths of many limb bones seem surprisingly low, in the light of the theory and of current knowledge of the fatigue properties of bone.

Accidents↗
PubMed1984

Stride length and speed for adults, children, and fossil hominids.

Research workers studying the relationship between stride length (L) and speed (u) in human walking have often expressed their results as multiples of stature (h): they have given values of L/h and u/h. They have claimed or implied that this takes account of differences of body size and that L/h should be the same function of u/h for people of all sizes. It is shown that this is not true for comparisons of children with adults. Further, it is argued by dimensional analysis that u/square root gh is a more appropriate speed parameter that u/h (g is the acceleration of free fall). It is shown that L/h is approximately the same function of u/square root gh for children aged 4 or more years as for adults. The empirical relationship between L/h and u/square root gh is used to make new estimates of walking speed for the early hominid footprints found at Laetoli, Tanzania. The speeds obtained are equivalent to mean speeds of human walking observed in small towns (i.e., they give approximately equal values of u/square root gh).

Adult↗
PubMed1981

Design of the mammalian respiratory system. VII. Scaling mitochondrial volume in skeletal muscle to body mass.

Since O2 is mainly consumed in muscle mitochondria during heavy physical work, one would expect to find a relationship between the volume density of mitochondria in skeletal muscles and maximal O2 uptake. We analyzed the volume density of mitochondria, Vv(mt,f) in four muscles of a series of African mammals ranging in body mass from 0.4 to 251 kg. Vv(mt,f) scaled as Mb-0.231, Mb-0.163, Mb-0.139 and Mb-0.055 in Mm. semitendinosus, longissimus dorsi, vastus medialis and diaphragm, respectively. The mass or volume of diaphragm was found to scale as Mb0.865, whereas for Mm. semitendinosus and vastus medialis, muscle volume (Vmu) scaled as Mb1.030 and Mb0.956 respectively. Scaling the absolute volume of mitochondria Vmt, in these muscles (Vmt = Vv (mt,f) x Vmu) against Mb gives regression lines whose slopes closely parallel that obtained for Vo2max against body mass. Therefore the ratio of volume of mitochondria in these muscles to Vo2max is body mass independent.

Africa↗
PubMed1978

Rebound resilience of tendons in the feet of sheep (Ovis aries).

The interosseous muscle of the fore foot of the sheep is multipennate, with large tendons but extremely short muscle fibres. It is believed to save energy in locomotion by elastic storage in its tendons and its sheath. Its rebound resilience (at 5-7 Hz and 20-37 degrees C) is about 0.62.

Animals↗
PubMed1977

Surgical treatment of urethral stricture.

We reviewed 59 cases of urethral stricture diseases treated at Charity Hospital of Louisiana in New Orleans from 1965 to 1975 to determine whether surgery was a feasible alternative to repeated urethral dilatations. Five different surgical procedures were done: internal urethrotomy, Johanson-Leadbetter, patch-graft, Turner-Warwich, and dismembered technics. Results of internal urethrotomy were poor, but the other procedures had an overall success of 72 percent.

Humans↗