Charles M. Tipton

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.

Neuroendocrine and Immune System Responses with Spaceflights

Despite the fact that the first human was in space during 1961 and individuals have existed in a microgravity environment for more than a year, there are limited spaceflight data available on the responses of the neuroendocrine and immune systems. Because of mutual interactions between these respective integrative systems, it is inappropriate to assume that the responses of one have no impact on functions of the other. Blood and plasma volume consistently decrease with spaceflight; hence, blood endocrine and immune constituents will be modified by both gravitational and measurement influences. The majority of the in-flight data relates to endocrine responses that influence fluids and electrolytes during the first month in space. Adrenocorticotropin (ACTH), aldosterone, and anti-diuretic hormone (ADH) appear to be elevated with little change in the atrial natriuretic peptides (ANP). Flight results longer than 60 d show increased ADH variability with elevations in angiotensin and cortisol. Although post-flight results are influenced by reentry and recovery events, ACTH and ADH appear to be consistently elevated with variable results being reported for the other hormones. Limited in-flight data on insulin and growth hormone levels suggest they are not elevated to counteract the loss in muscle mass. Post-flight results from short- and long-term flights indicate that thyroxine and insulin are increased while growth hormone exhibits minimal change. In-flight parathyroid hormone (PTH) levels are variable for several weeks after which they remain elevated. Post-flight PTH was increased on missions that lasted either 7 or 237 d, whereas calcitonin concentrations were increased after 1 wk but decreased after longer flights. Leukocytes are elevated in flights of various durations because of an increase in neutrophils. The majority of post-flights data indicates immunoglobulin concentrations are not significantly changed from pre-flight measurements. However, the numbers of T-lymphocytes and natural killer cells are decreased with post-flight conditions. Of the lymphokines, interleukin-2 production, lymphocyte responsiveness, and the activity of natural killer cells are consistently reduced post-flight. Limited head-down tilt (HDT) data suggest it is an effective simulation model for microgravity investigations. Neuroendocrine and pharmacological countermeasures are virtually nonexistent and should become high priority items for future research. Although exercise has the potential to be an effective countermeasure for various neuroendocrine-immune responses in microgravity, this concept must be tested before flights to Mars are scheduled.

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.

Measurement of Ligamentous Strength in Rat Knees

Data have been presented relative to the strength and force-elongation relationships of rat ligaments. The findings indicated that the testing methods employed are sufficiently reliable for experimental purposes. Results showed that body weight, sex, and age of the animals are important parameters w

Effects of exercise training on responses to central injection of CRF and noise stress.

The purpose of this study was to test the hypothesis that the cardiovascular and sympathoadrenal responses to acute environmental stress are attenuated by exercise training. Furthermore, we tested the hypothesis that the cardiovascular and sympathoadrenal responses to intracerebroventricular (ICV) administration of corticotropin-releasing factor (CRF) would be attenuated by training. Conscious, unrestrained, male Sprague-Dawley rats assigned to either a treadmill trained (16-26 m/min, 30-60 min/day, 5 days/week) or nontrained (16-26 m/min, 10 min/day, 1 day/week) group were studied. After 8-10 weeks of training, maximal oxygen uptake was significantly higher in the trained (108 +/- 3 ml/kg/min) vs. the nontrained (94 +/- 4 ml/min/kg) group. There were no significant differences in baseline mean arterial pressure, heart rate and plasma catecholamine levels associated with training. Trained rats exhibited significantly attenuated elevations in arterial pressure (20 +/- 3 vs. 36 +/- 2 mmHg for nontrained) and heart rate (-3 +/- 3 vs. 12 +/- 5 beats/min for nontrained) in response to acute noise stress. Twenty minutes after ICV administration of CRF, blood pressure (trained = 119 +/- 2 mmHg, nontrained = 127 +/- 2 mmHg), heart rate (trained = 408 +/- 8 beats/min, nontrained = 424 +/- 10 beats/min), plasma norepinephrine levels (trained = 757 +/- 54 pg/ml, nontrained = 775 +/- 100 pg/ml) and plasma epinephrine levels (trained = 266 +/- 29 pg/ml, nontrained = 225 +/- 42 pg/ml) were significantly elevated in both trained and nontrained groups. CRF-induced elevations of blood pressure, but not heart rate or plasma catecholamine levels, were significantly attenuated in the trained group.(ABSTRACT TRUNCATED AT 250 WORDS)

Work and metabolic patterns of fast and slow twitch skeletal muscle contractingin situ

SummaryA study was conducted to compare the work capacity and aerobic and anaerobic metabolic profiles of the fast-twitch tibialis anterior and slow-twitch soleus muscles of the rat stimulated to contractin situ. Results showed that the soleus could sustain greater relative and absolute work levels than the tibialis anterior. Metabolic profiles revealed that the tibialis anterior depended on anaerobic pathways to a greater extent than the soleus, since greater amounts of phosphocreatine were depleted and greater amounts of glycogen were broken down and metabolized to lactate in the tibialis anterior. The ability of both muscles to sustain prolonged work was attributed to the high capacity of red and intermediate muscle for fatty acid oxidation as evidenced by the higher levels of resting and exercise acyl-carnitine and the greater activity levels of carnitine palmityltransferase measured in the soleus.

Influence of exercise training on the oxidative capacity of rat abdominal muscles.

Our purpose was to determine if endurance exercise training would increase the oxidative capacity of the abdominal expiratory muscles of the rat. Accordingly, 9 male rats were subjected to an endurance training protocol (1 h/day, 6 days/week, 9 weeks) and 9 litter-mates served as controls. Citrate synthase (CS) activity was used as an index of oxidative capacity, and was determined in the following muscles: soleus, plantaris, costal diaphragm, crural diaphragm, and in all four abdominal muscles: rectus abdominis, transversus abdominis, external oblique, and internal oblique. Compared to their non-trained litter-mates, the trained rats had higher peak whole body oxygen consumption rates (+ 16%) and CS activities in plantaris (+34%) and soleus (+36%) muscles. Thus, the training program caused substantial systemic and locomotor muscle adaptations. The CS activity of costal diaphragm was 20% greater in the trained animals, but no difference was observed in crural diaphragm. The CS activity in the abdominal muscles was less than one-half of that in locomotor and diaphragm muscles, and there were no significant changes with training except in the rectus abdominis where a 26% increase was observed. The increase in rectus abdominis CS activity may reflect its role in postural support and/or locomotion, as none of the primary expiratory pumping muscles adapted to the training protocol. The relatively low levels of CS activity in the abdominal muscles suggests that they are not recruited frequently at rest, and the lack of an increase with training indicates that these muscles do not contribute significantly to the increased ventilatory activity accompanying exercise in the rat.

Iowa wrestling study: weight loss and urinary profiles of collegiate wrestlers.

A longitudinal study was conducted with various members of the 1975 University of Iowa NCAA championship wrestling team to determine if excessive weight loss, accompanied by signs of dehydration, occurred at the college level of competition. Body weight changes from September to December indicated a mean loss of 6%, while skinfold totals (6 sites) changed from a mean of 58 mm to 37 mm. During a four-month period, mean weight losses of 10.2, 9.5, 8.0, 7.5 and 7.0 lbs occurred in intervals of 12, 4, 3, 2 and 1 day, respectively. Basal urines analyzed throughout the season usually contained 2-3 times the potassium excreted before the season started. Analyses of urines at various intervals during a 2-day time period prior to weigh-in showed a .003 increase in specific gravity, 160 mosm/1 increase in osmolarity, .10 decrease in pH, 45.3 mEq/1 decrease in Na+ concentration, and a 71.3 mEq/1 increase in K+ concentration which suggested that the wrestlers were dehydrated prior to competition. Total urinary electrolyte loss during the 2 days amounted to 3.7% of estimated total body Na+ stores and 3.0% of total body K+ stores. These data were similar to what had been reported for Iowa high school finalists and indicated that collegiate wrestlers were also competing while in a dehydrated state.