Ronald D. Matthes

The influence of physical activity on ligaments and tendons.

Using either a bone-ligament-bone or a muscle-tendon-bone preparation, numerous investigators have demonstrated that the usual site of separation is in the transitional zone between the ligament (or tendon) and bone; hence, the term junction strength or load at separation is used to describe functional changes in these preparations. Junction strength is decreased with inactivity (immobilization) and increased with chronic activity (training) provided that the exercise program is of an endurance nature. Training also increases junction strength in thyroidectomized and hypophysectomized rats. Besides in junction strength, training results in heavier ligaments and higher ligament weight/length ratios. However, water content, collagen concentrations/dry weight or collagen concentration per weight/length unit are not significantly influenced by repeated bouts of exercise. Although immobilization is associated with lower elastic stiffness values (kg/mm), training appears to have little influence on this measure in normal animals. Rats and dogs with surgically repaired ligaments are weaker and the strength results are markedly lower if the leg is immobilized. Exercise training improves the repair strength of ligaments but does not result in normal values twelve weeks after the surgery. Exogenous administration of ICSH or testosterone results in higher repair strength whereas TSH, thyroxine, ACTH and growth hormone decreases this measure. It was concluded that the mechanical stress produced by chronic exercise is an important determination of the strength of repaired ligaments and of the junctions between ligaments (or tendons) and bones.

Influence of Physical Activity on Ligament Insertions in the Knees of Dogs

1. At ligament-bone junctions in dogs existing at varying levels of physical activity, strength diminished as activity diminished. 2. At the proximal end of the tibia, subperiosteal resorption weakened the ligament-bone junction of the medical collateral ligament. A similar change was seen in the fibular attachment of the lateral collateral ligament but not in the other ligament attachments about the knee. 3. Microscopically, widespread subperiosteal bone resorption developed in inactive dogs. 4. Simple caging for six weeks or more produed boen resorption. 5. With continued caging, bone resorption at the ligament-bone attachment healed over a period of six months or more as fibrous tissue replaced resorbed bone and then became mineralized. The widespread subperiosteal bone loss consequent to inactivity probably healed in the same way, suggesting on the basis of this histological evidence that inactivity produces bone resorption which is followed by bone accretion.

An in situ study of the influence of a sclerosing solution in rabbit medial collateral ligaments and its junction strength.

A double-blind study was conducted to assess the influence of a sclerosing solution on rabbit medial collateral ligaments (MCL) in situ. It was shown that repeated injections of 5% sodium morrhuate into the MCL and its bony attachments significantly increased its bone-ligament-bone junction strength, ligament mass and thickness when compared to saline-injected controls. Morphometric analysis of electron micrographs showed a highly significant corresponding increase of the collagen fibril diameters in the experimental ligament compared against the control MCL. These composite findings suggested that the sclerosing solution had a significant influence on dense connective tissue at the insertion sites. The mechanisms for these changes are uncertain and are the basis for future investigations.

Influence of age and sex on the strength of bone-ligament junctions in knee joints of rats.

The bone-ligament junction strength of femur-medial collateral ligament-tibia complexes in rats was measured in situ at various ages during a two-year period. Male rats had a higher junction strength than female rats, a difference that became apparent when the animals were sixty days old and in male but not female animals subsequently paralleled the changes in body weight. However, on a bodyweight basis, the junctions were stronger in female than in male rats and this sex difference was evident at fifteen days old and persisted thereafter. Regression analysis between body weight and junction strength indicated that female rats had a significantly higher slope than males, which suggested that the sex differences were due to a hormonal factor or factors. Other measurements showed that elastic stiffness, failure energy, and collagen concentration in the ligament increased, whereas the water content of the ligament decreased with age. Most of these changes could be attriubted to the aging process and not the sex of the animal. It was concluded, however, that the strength of the insertion sites of ligaments on bones are responsive to the hormonal fluctuations that occur with aging.

Influence of training on the blood pressure changes during lower body negative pressure in rats.

The responses of non-trained and endurance-trained rats to conditions of lower body negative pressure (LBNP) was evaluated in normotensive, borderline hypertensive, and genetic hypertensive groups, as well as in sub-groups subjected to conditions of ventilation with 100% oxygen, systematic hemorrhaging, or sino-aortic denervations. Compared to their non-trained controls, normotensive trained rats exhibited significantly greater and faster falls in arterial blood pressure. This finding suggested a change in baroreceptor sensitivity. Related, but not statistically significant trends were observed with the hypertensive groups. Borderline hypertensive rats (DOCA injections) did not demonstrate any of these differences. Measurements of blood changes during the LBNP procedure and the effects of inspiring 100% oxygen indicated that the aortic and carotid chemoreceptors were not responsible for this training effect. After baroreceptor denervation, the group differences were abolished. In addition, the training effects were generally absent when hemorrhaging was performed, a result suggesting a difference in compliance. We have concluded from these results that endurance training will be associated with greater decreases in arterial blood pressure during LBNP than will be experienced by non-trained populations. However, the responsible mechanisms are unclear and will require further investigation.

The response of the Galago senegalensis to physical training

Abstract 1. 1. Investigations were undertaken to determine the effects of a 20-week exercise training program with the Galayo senegalensis and whether the adaptations noted were similar to those reported for humans, dogs or rats. 2. 2. Using a treadmill program capable of eliciting heart rate in excess of 500 beats/min or rectal temperatures higher than 41°C, it was found that training produced bradycardia, lower resting blood pressures, elevated muscle, ligament and tendon cytochrome oxidase activity, higher medial collateral ligament weight/length ratios and an increased strength of the patellar ligament and the tendon from extensor muscles. 3. 3. However, training had no statistical influence on organ weights, bone-ligament junction strength. adipocyte diameters or upon several weight/length ratios or strength measurements from other ligaments and tendons. 4. 4. From these results, we concluded that the Galayo senegalensis could be a useful animal model to study selective mechanisms associated with chronic exercise: however, caution was necessary before one could extrapolate the findings to humans.

Hydroxyproline Concentrations in Ligaments From Trained and Nontrained Rats

In recent years numerous laboratories have demonstrated that repeated bouts of exercise (training) will cause the junction strength of bone-ligament-bone preparations to increase [14-17, 19, 21-23]. Similar findings have been reported from measurements of isolated tendons [20]. The biochemical explanation for these changes, specifically as it pertains to bone-ligament-bone preparations, is complex because the point of separation occurs within a transition zone involving ligament-nonmineralized fibrocartilage-mineralized fibrocartilage-bone [15]. Since the structure and function of connective tissue is dependent upon the amount, proportions, and interactions between collagen, elastin, non-collagen proteins and glycoaminoglycans [10], we initiated studies on the influence of training on collagen concentration in ligaments to gain a better understanding of the mechanism responsible for the effects of training. Collagen represents approximately 80% of the dried weight of tendons and essentially 14% of the amino acid residues present in collagen are hydroxyproline [6, 13]. Since hydroxyproline is found almost exclusively within collagen, its measurement can be used to depict changes in the concentration of collagen in tissues from experimental animals [8, 12, 13].