Response of compressed skinned skeletal muscle fibers to conditions that simulate fatigue

During fatigue, muscles become weaker, slower, and more economical at producing tension. Studies of skinned muscle fibers can explain some but not all of these effects, and, in particular, they are less economical in conditions that simulate fatigue. We investigated three factors that may contribute to the different behavior of skinned fibers. 1) Skinned fibers have increased myofilament lattice spacing, which is reversible by osmotic compression. 2) A myosin subunit becomes phosphorylated during fatigue. 3) Inosine 5'-monophosphate (IMP) accumulates during fatigue. We tested the response of phosphorylated and unphosphorylated single skinned fibers (isometric tension, contraction velocity, and adenosinetriphosphatase activity) to changes in lattice spacing (0-5% dextran) and IMP (0-5 mM) in the presence of altered concentrations of P(i) (3-25 mM), H+ (pH 7-6.2), and ADP (0-5 mM). The response of maximally activated skinned fibers to the direct metabolites of ATP hydrolysis is not altered by osmotic compression, phosphorylating myosin subunits, or increasing IMP concentration. These factors, therefore, do not explain the discrepancy between intact and skinned fibers during fatigue.

Metabolic and performance adaptations to interval training in endurance-trained cyclists

This study examined the effects of sustained high-intensity interval training (HIT) on the athletic performances and fuel utilisation of eight male endurance-trained cyclists. Before HIT, each subject undertook three baseline peak power output Wpeak tests and two simulated 40-km time-trial cycling performance (TT40) tests, of which the variabilities were 1.5 (1.3)% and 1.0 (0.5)%, respectively [mean (SD)]. Over 6 weeks, the cyclists then replaced 15 (2)% of their 300 (66) km.week-1 endurance training with 12 HIT sessions, each consisting of six to nine 5-min rides at 80% of Wpeak, separated by a l-min recovery. HIT increased Wpeak from 404 (40) to 424 (53) W (P < 0.01) and improved TT40 speeds from 42.0 (3.6) to 43.0 (4.2) km.h-1 (P < 0.05). Faster TT40 performances were due to increases in both the absolute work rates from 291 (43) to 327 (51) W (P < 0.05) and the relative work rates from 72.6 (5.3)% of pre-HIT Wpeak to 78.1 (2.8)% of post-HIT Wpeak (P < 0.05). HIT decreased carbohydrate (CHO) oxidation, plasma lactate concentration and ventilation when the cyclists rode at the same absolute work rates of 60, 70 and 80% of pre-HIT Wpeak (P < 0.05), but not when they exercised at the same relative (% post-HIT Wpeak) work rates. Thus, the ability of the cyclists to sustain higher percentages of Wpeak in TT40 performances after HIT was not due to lower rates of CHO oxidation. Higher relative work rates in the TT40 rides following HIT increased the estimated rates of CHO oxidation from approximately 4.3 to approximately 5.1 g.min-1.

Skeletal muscle buffering capacity and endurance performance after high-intensity interval training by well-trained cyclists

Skeletal muscle buffering capacity (beta m), enzyme activities and exercise performance were measured before and after 4 weeks of high-intensity, submaximal interval training (HIT) undertaken by six well-trained competitive cyclists [mean maximal oxygen consumption (VO2max) = 66.2 ml.kg-1.min-1]. HIT replaced a portion of habitual endurance training and consisted of six sessions, each of six to eight repetitions of 5 min duration at 80% of peak sustained power output (PPO) separated by 1 min of recovery. beta m increased from 206.6 (17.9) to 240.4 (34.1) mumol H+.g muscle dw-1.pH-1 after HIT (P = 0.05). PPO, time to fatigue at 150% PPO (TF150) and 40-km cycle time trial performance (TT40) all significantly improved after HIT (P < 0.05). In contrast, there was no change in the activity of either phosphofructokinase or citrate synthase. In addition, beta m correlated significantly with TT40 performance before HIT (r = -0.82, P < 0.05) and the relationship between change in beta m and change in TT40 was close to significance (r = -0.74). beta m did not correlate with TF150. These results indicate that beta m may be an important determinant of relatively short-duration (< 60 min) endurance cycling activity and responds positively to just six sessions of high-intensity, submaximal interval training.

Improved athletic performance in highly trained cyclists after interval training

This study determined whether a 4-wk high-intensity interval training program (HIT) would improve the 40-km time trial performances (TT40) of 8 competitive cyclists (peak O2 uptake 5.2 +/- 0.4 I.min-1) with a background of moderate-intensity endurance training (BASE). Before intervention, all cyclists were tested on at least three separate occasions to ensure that their baseline performances were stable. In these tests, peak sustained power output (PPO) was measured during a progressive exercise test, muscular resistance to fatigue was determined during a timed ride to exhaustion at 150% of PPO (TF150), and a TT40 was performed on a cycle-simulator. The coefficient of variation for all baseline tests was < 1.7 +/- 1.3% (mean +/- SD). Cyclists then replaced 15 +/- 2% of their approximately 300 km.wk-1 BASE training with HIT, which took place on 6 d and consisted of six to eight 5-min repetitions at 80% of PPO, with 60-s recovery between work bouts. HIT significantly improved TT40 (56.4 +/- 3.6 vs 54.4 +/- 3.2 min; P < 0.0001), PPO (416 +/- 32 vs 434 +/- 34 W; P < 0.01) and TF150 (60.5 +/- 9.3 vs 72.5 +/- 7.6 s; P < 0.01). The faster TT40 was due to a significant increase in both the cyclists' absolute (301 +/- 42 vs 326 +/- 43 W; P < 0.0001) and relative (72.1 +/- 5.6 vs 75.0 +/- 6.8% of PPO; P < 0.05) power output after HIT. These results indicate that a 4-wk program of HIT increased the PPO and fatigue resistance of competitive cyclists and improved their 40-km time trial performances.

Skeletal muscle buffering capacity is higher in the superficial vastus than in the soleus of spontaneously running rats

Skeletal muscle buffering capacity (beta mtitr) was determined in soleus (type I) and superficial vastus (type II) muscles of 16 Long-Evans rats with differing levels of spontaneous activity and in 11 sedentary control rats. beta mtitr was 24% higher (P < 0.001) in superficial vastus muscle than in soleus muscle (268 +/- 50 vs. 216 +/- 30 mumol H+ g muscle dry wt-1 pH unit-1) (mean +/- SD). There was no relationship between beta mtitr and mean weekly running distance amongst spontaneously running rats, nor was beta mtitr any greater in these rats than in a group of sedentary control rats. Protein to wet wt ratio was 31% higher (P < 0.0001) in the superficial vastus muscle when compared with soleus muscle (22.04 +/- 3.74 vs. 16.77 +/- 3.00 mg protein, 100 mg wet wt muscle-1), but there was no relationship between protein to wet wt ratio and running distance. Initial muscle homogenate pH (pHi) was lower in superficial vastus muscle compared with soleus muscle (6.36 +/- 0.25 vs. 6.63 +/- 0.16). Running rats had a significantly lower pHi in both soleus and superficial vastus than sedentary controls. There was an exponential relationship between weekly running distance and pHi in both the superficial vastus muscle (r = -0.86. P < 0.001) and the soleus muscle (r = -0.73, P < 0.01). Citrate synthase activity correlated with weekly running distance in superficial vastus muscle (r = 0.66, P < 0.01) but not in soleus muscle. The results confirm a higher beta mtitr in the type II superficial vastus muscle when compared with the predominantly type I soleus muscle. We suggest that this may be partly the result of a higher protein concentration in type II muscle. Future studies measuring beta mtitr in mixed muscle (e.g. human vastus lateralis) should report fibre type composition.

Nucleotide turnover rate measured in fully relaxed rabbit skeletal muscle myofibrils

Steady state measurements of the ATP turnover rate of myosin crossbridges in relaxed living mammalian muscle or in in vitro systems are complicated by other more rapid ATPase activities. To surmount these problems we have developed a technique to measure the nucleotide turnover rate of fully relaxed myosin heads in myofibrils using a fluorescent analogue of ATP (mant-ATP). Rabbit myofibrils, relaxed in 1.6 mM ATP, were rapidly mixed with an equal volume of solution containing 80 microM mant-ATP and injected into a fluorimeter. As bound ADP is released, a fraction of the myosin active sites bind mant-ATP and fluorescence emission rises exponentially, defining a rate of nucleotide turnover of 0.03 +/- 0.001 s-1 at 25 degrees C (n = 17). This rate was approximately equal to one half that of purified myosin. The turnover rates for myosin and myofibrils increased between 5 degrees and 42 degrees C, reaching 0.16 +/- 0.04 s-1 and 0.06 +/- 0.005 s-1, respectively, at 39 degrees C, the body temperature of the rabbit. If the rate observed for purified myosin occurred in vivo, it would generate more heat than is observed for resting living muscle. When myosin is incorporated into the myofilament lattice, its ATPase activity is inhibited, providing at least a partial explanation for the low rate of heat production by living resting muscle.

Bone mineral density in mature, premenopausal ultramarathon runners

We measured bone mineral density (BMD) in 25 premenopausal ultramarathon (56 km) runners aged 29-39 yr and related risk factors for decreased BMD with actual BMD. Fifteen runners who had never had oligo/amenorrhea (R) were compared with 10 runners (OA): 4 oligomenorrheic, 2 amenorrheic, and 4 with prior oligo/amenorrhea. Menstrual, dietary and training data were obtained. BMD of the lumbar spine (LS) and proximal femur (F) were measured by dual energy x-ray densitometry. Both groups had similar body mass (58 +/- 8 vs 57 +/- 8 kg), running and dietary histories. F BMD was not different (P = 0.07) and correlated only with BMI (P < 0.05; r = 0.43). LS BMD was lower in OA (0.946 +/- 0.098 g.cm-2) than R (1.088 +/- 0.069 g.cm-2; P < 0.001). Menstrual History Index (MHI), (estimated periods.yr-1 since age 13), was higher in R (11.6 +/- 0.6) than OA (9.4 +/- 2.1; P < 0.01). LS BMD correlated with MHI (P < 0.0005; r = 0.67) and years oligomenorrheic (P < 0.01; r = -0.58) but not years amenorrheic, parity, breastfeeding, diet, or training. In conclusion, in mature women distance runners low LS BMD is related to a history of oligo/amenorrhea regardless of resumption of regular menstrual cycles in some subjects. Not only amenorrhea, but also prolonged oligomenorrhea may negatively influence peak adult bone mass.

Age-related differences in cross-sectional geometry of the forearm bones in healthy women

Men exhibit age-related adaptive changes in long bone geometry, namely, endosteal resorption and periosteal apposition of bone, that help to preserve bone strength. It is not clear whether women undergo similar adaptive responses. To address this question, we assessed the bone mineral density and cross-sectional geometry of the radius and ulna at the one-third distal site by single photon absorptiometry and computed tomography (CT) in healthy young (n = 21, age 20-30 years) and older (n = 22, age 63-84 years) women. We used the CT data to compute the total subperiosteal, medullary, and cortical areas, as well as the maximum, minimum, and polar moments of inertia. We normalized the geometric parameters for bone length and performed comparisons using both the original and size-corrected data. Radial and ulnar bone mineral content and density were 20-30% lower in the older women (P < 0.0001). Ulnar width, total area, medullary area, and maximum and polar moment of inertia were greater in the older than in the younger women. Although we observed similar trends when we examined the radius data that were corrected for bone size, age-related differences in radial geometry were less pronounced and were not significant. We conclude that women undergo endosteal resorption and periosteal apposition of the ulna with age, thereby exhibiting an adaptive pattern that helps to preserve bone strength. The different behavior of these two bones suggests that local, rather than systemic, factors underlie this adaptation.

Low bone mineral density at axial and appendicular sites in amenorrheic athletes

Amenorrheic athletes have low axial bone-mineral density (BMD, g.cm-2). We compared 12 amenorrheic and 9 eumenorrheic women athletes to determine whether athletes with amenorrhea have lower BMD in other skeletal regions, including weight-bearing lower limbs. BMD was measured by dual energy x-ray and single photon absorptiometry. Both groups had similar age, body mass, and exercise quantity. Women with amenorrhea missed 86.3 +/- 58.3 menstrual periods since menarche. BMD was lower in the amenorrheic vs eumenorrheic subjects for the lumbar spine (0.928 +/- 0.056 vs 1.050 +/- 0.110, P < 0.005), whole body (1.032 +/- 0.05 vs 1.09 +/- 0.06, P < 0.05), most regions of the whole body (P < 0.05-0.001), all areas of the proximal femur (P < 0.005), and at the femoral mid-shaft (1.333 +/- 0.109 vs 1.491 +/- 0.088, P < 0.005). No significant differences were detected at the mid-radius and tibial shaft. The best predictors of BMD were years of regular menstruation for lumbar spine; and years of amenorrhea for hip, femoral mid-shaft, and whole body. We conclude that low BMD in athletes with amenorrhea is not limited to the axial skeleton but is also present in other regions including appendicular weight-bearing bones.

Influence of recreational activity and muscle strength on ulnar bending stiffness in men

Bone bending stiffness (modulus of elasticity [E] x moment of inertia [I]), a measure of bone strength, is related to its mineral content (BMC) and geometry and may be influenced by exercise. We evaluated the relationship of habitual recreational exercise and muscle strength to ulnar EI, width, and BMC in 51 healthy men, 28-61 yr of age. BMC and width were measured by single photon absorptiometry and EI by mechanical resistance tissue analysis. Maximum biceps strength was determined dynamically (1-RM) and grip strength isometrically. Subjects were classified as sedentary (S) (N = 13), moderately (M) (N = 18), or highly active (H) (N = 20) and exercised 0.2 +/- 0.2; 2.2 +/- 1.3; and 6.8 +/- 2.3 h.wk-1 (P < 0.001). H had greater biceps (P < 0.0005) and grip strength (P < 0.05), ulnar BMC (P < 0.05), and ulnar EI (P = 0.01) than M or S, who were similar. Amount of activity correlated with grip and biceps strength (r = 0.47 and 0.49; P < 0.001), but not with bone measurements, whereas muscle strength correlated with both EI and BMC (r = 0.40-0.52, P < 0.005). EI also correlated significantly with both BMC and ulnar width (P < 0.0001). Ulnar width and biceps strength were the only independent predictors of EI (r2 = 0.67, P < 0.0001). We conclude that levels of physical activity sufficient to increase arm strength influence ulnar bending stiffness.

In vivo assessment of forearm bone mass and ulnar bending stiffness in healthy men

The cross-sectional bending stiffness EI of the ulna was measured in vivo by mechanical resistance tissue analysis (MRTA) in 90 men aged 19-89 years. MRTA measures the impedance response of low-frequency vibrations to determine EI, which is a reflection of elastic modulus E and moment of inertia I for the whole ulna. EI was compared to conventional estimates of bone mineral content (BMC), bone width (BW), and BMC/BW, which were all measured by single-photon absorptiometry. Results obtained from the nondominant ulna indicate that BW increases (r = 0.27, p = 0.01) and ulnar BMC/BW decreases (r = -0.31, p < or = 0.005) with age. Neither BMC nor EI declined with age. The single best predictor of EI was BW (r2 = 0.47, p = 0.0001), and further small but significant contributions were made by BMC (r2 = 0.53, p = 0.0001) and grip strength (r2 = 0.55, p = 0.0001). These results suggest that the resistance of older men to forearm fracture is related to age-associated changes in the moment of inertia achieved by redistributing bone mineral farther from the bending axis. We conclude that the in vivo assessment of bone geometry offers important insights to the comprehensive evaluation of bone strength.

Are Risk Factors for Menstrual Dysfunction Cumulative?

In brief That so many factors are associated with menstrual dysfunction JMBJ in athletes makes management difficult. This study compares the number and prevalence of risk factors in ultramarathon runners who had menstrual dysfunction with those in matched controls who had no history of menstrual dysfunction. Both groups had statistically similar prevalences of the risk factors analyzed, but the runners with menstrual dysfunction had significantly more risk factors. Also, significantly more of them had three or more risk factors. The results indicate that no single factor is critical and suggest that management should focus on reducing the number of risk factors.

Metabolic rate, not percent dehydration, predicts rectal temperature in marathon runners

This study was designed to determine the factors predicting the post-race rectal temperature in marathon runners. Post-race rectal temperatures of 30 recreational runners (maximum oxygen consumption (VO2max) = 58.3 +/- 5.9 ml O2.kg-1.min-1; mean +/- SD) who completed a 42.2 km marathon at 75.8% (+/- 9.3%) VO2max were measured and related to their levels of dehydration (percent mass loss), their running velocities (km.h-1), and their estimated absolute metabolic rates (1 O2.min-1) for different segments of the 42.2 km race. The influence of certain anthropometric variables was also determined. Percent mass loss during the race (2.5 +/- 1.4%), post-race rectal temperatures (38.9 +/- 0.6 degrees C), and rates of sweat loss (1.0 +/- 0.3 1.h-1) were low. There was no statistical relationship between percent mass loss and post-race rectal temperature. Post-race rectal temperatures were significantly related to the metabolic rates for the full 42.2 km and for the last 21.1 and 6 km of the race, and to the average running velocity for the last 6 km (P less than 0.05 and P less than 0.01). Average sweat rates were related to metabolic rates for 42.2 km and for the last 6 km of the race (P less than 0.05) but were unrelated to running velocity. We conclude that metabolic rate sustained during the latter section of the race, and not the level of dehydration, is the principal determinant of the post-race rectal temperature in marathon runners.

Low bone density is an etiologic factor for stress fractures in athletes

OBJECTIVE

To determine whether low bone density and other risk factors for osteoporosis are associated with stress fractures in athletes.

DESIGN

Case-control study.

SETTING

Institutional sports injury clinic with primary and secondary care.

PARTICIPANTS

Twenty-five athletes (nineteen women) with scintigraphically confirmed stress fractures matched for sex, age, weight, height, and exercise history with 25 control athletes with no history of bone injury.

MEASUREMENTS AND MAIN RESULTS

Bone mineral density measured by dual-energy x-ray absorptiometry was significantly lower in athletes with fractures than in control athletes: In the spine, bone mineral density was 1.01 +/- 0.14 g/cm2 in athletes with fractures and 1.11 +/- 0.13 g/cm2 in control athletes (P = 0.02). In the femoral neck, it was 0.84 +/- 0.09 g/cm2 in athletes with fractures and 0.90 +/- 0.11 g/cm2 in control athletes (P = 0.005). It was also significantly lower in the Ward triangle (P = 0.01) and the greater trochanter (P = 0.01). Eight athletes with fractures and no control athletes had less than 90% of predicted age-related spine density (P = 0.01), and three athletes with fractures had bone mineral densities that were 2 SDs or more below this predicted level. More athletes with fractures than control athletes had current menstrual irregularity (amenorrhea or oligomenorrhea) (P less than 0.005). Fewer athletes with fractures were using oral contraceptives (P less than 0.05). Seven-day diet records indicated similar energy and nutrient intakes, except athletes with fractures had lower calcium intakes (697 +/- 242 mg/d compared with 832 +/- 309 mg/d; P = 0.02). Dairy product intake was lower in athletes with fractures since leaving high school (P less than 0.05). The incidence of a family history of osteoporosis was similar in both groups.

CONCLUSIONS

In athletes with similar training habits, those with stress fractures are more likely to have lower bone density, lower dietary calcium intake, current menstrual irregularity, and lower oral contraceptive use.

Plasma volume and renal function during and after ultramarathon running

Plasma volume (PV) and renal function were studied in eight subjects for 3 d prior to and 6 d after a 56 km footrace. Immediately following the race, PV, creatinine clearance, and urine flow were unchanged from pre-race values. Over the subsequent 3 d, PV increased due initially to a 17 g influx of serum albumin and an associated increase in plasma sodium content, which persisted throughout the study period. A reduction in urine sodium secretion occurred during the race day. Creatinine clearance increased after the race and remained elevated for 48 h. Increases serum enzyme activities, C-reactive protein concentration, serum uric acid content, and plasma creatinine concentration and production suggest muscle damage. We suggested the following. First, the persistent post-exercise plasma volume expansion is initiated by an influx of albumin into the intravascular space with an associated increase in plasma sodium content. A decrease in urine sodium excretion during the race day would contribute to the latter. Second, the interpretation of post-race changes in serum constituents must take account of changes in plasma volume. Third, there is an increase in creatinine clearance, indicating an increase in glomerular filtration rate, after both standard and ultramarathon running. This may be caused by the products of muscle cell damage although the physiologic mechanism for this is unclear.

Skeletal muscle limits the exercise tolerance of renal transplant recipients: effects of a graded exercise training program

Sixteen renal transplant recipients were studied before and after they had participated in a 24-week exercise training program to determine (1) the nature of the factors explaining their impaired exercise tolerance, and (2) their adaptative responses to exercise training. During progressive treadmill exercise to exhaustion prior to training, renal transplant recipients stopped exercising at lower peak rates of oxygen consumption (VO2max) (29.0 +/- 7.8 47.9 +/- 9.1 mL O2.kg-1.min-1; P less than 0.001) and ventilation (55.9 +/- 13.2 v 124.0 +/- 22.2 L.min-1; P less than 0.0001), and at lower peak heart rates (169 +/- 22 v 196 +/- 9 beats.min-1; P less than 0.05) and peak blood lactate concentrations (5.0 +/- 2.1 v 11.5 +/- 4.0 mmol.L-1; P less than 0.001) than did controls. None showed a plateau in oxygen consumption with increasing workload. Exercise time to exhaustion was also significantly shorter in renal transplant recipients (9.5 +/- 1.8 v 16.0 +/- 1.3 min; P less than 0.0001). After training, exercise time to exhaustion (12.0 +/- 2.0 min; P less than 0.001), VO2max (37.5 +/- 4.8 mL O2.kg-1.min-1; P less than 0.05), maximum ventilation rate (68.5 +/- 14.0 L.min-1; P less than 0.05), peak blood lactate concentrations (7.8 +/- 1.8 mmol-L-1; P less than 0.001), and the rate of oxygen consumption at a blood lactate concentration of 2.0 mmol.L-1 (22.5 +/- 2.5 v 16.5 +/- 2.2 mL O2.kg-1.min-1; P less than 0.001) had all increased significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Peak treadmill running velocity during the VO2 max test predicts running performance

Twenty specialist marathon runners and 23 specialist ultra-marathon runners underwent maximal exercise testing to determine the relative value of maximum oxygen consumption (VO2max), peak treadmill running velocity, running velocity at the lactate turnpoint, VO2 at 16 km h-1, % VO2max at 16 km h-1, and running time in other races, for predicting performance in races of 10-90 km. Race time at 10 or 21.1 km was the best predictor of performance at 42.2 km in specialist marathon runners and at 42.2 and 90 km in specialist ultra-marathon runners (r = 0.91-0.97). Peak treadmill running velocity was the best laboratory-measured predictor of performance (r = -0.88(-)-0.94) at all distances in ultra-marathon specialists and at all distances except 42.2 km in marathon specialists. Other predictive variables were running velocity at the lactate turnpoint (r = -0.80(-)-0.92); % VO2max at 16 km h-1 (r = 0.76-0.90) and VO2max (r = 0.55(-)-0.86). Peak blood lactate concentrations (r = 0.68-0.71) and VO2 at 16 km h-1 (r = 0.10-0.61) were less good predictors. These data indicate: (i) that in groups of trained long distance runners, the physiological factors that determine success in races of 10-90 km are the same; thus there may not be variables that predict success uniquely in either 10 km, marathon or ultra-marathon runners, and (ii) that peak treadmill running velocity is at least as good a predictor of running performance as is the lactate turnpoint. Factors that determine the peak treadmill running velocity are not known but are not likely to be related to maximum rates of muscle oxygen utilization.

The influence of inborn athletic potential on choice of profession and exercise habits of paramedical students

Twenty physiotherapy and 15 pharmacology students from the 2nd-year paramedical class were studied to determine whether inborn athletic potential had influenced their choice of profession. Each subject completed a questionnaire and performed a graded treadmill test to exhaustion to determine maximum oxygen consumption (VO2max), peak treadmill running velocity and ventilation threshold (VT). No difference was found between physiotherapy and pharmacy students in body mass, VO2max or running speed at VT, but physiotherapy students reached a higher peak treadmill velocity (P less than 0.01). Fewer pharmacy students participated in sport at university. To determine factors influencing participation in sport, students from both groups who exercised were compared with non-exercisers. Students who exercised had significantly higher VO2max, peak treadmill running velocity and VT, but differences were less than could be explained purely on the basis of superior genetic endowment. It is concluded: (i) that physiotherapy students do not have greater inborn athletic potential than pharmacy students; (ii) that exercising students show physiological adaptations compatible with a higher level of 'fitness', and (iii) that whereas lack of inborn athletic potential is not the reason why some students do not exercise regularly at university, inborn athletic potential may determine those who will exercise competitively.

Effect of exercise on the development of osteoporosis in adult rats

The role of moderate exercise in the prevention of high-turnover osteoporosis was investigated by the use of an animal model. The effect of chronic training on gravimetric, mineral, physical, and histological parameters of normal bone was also examined. Fifty-six adult female Long-Evans rats were divided into four groups: sedentary (C) and exercising controls (E) and sedentary (O) and exercising osteoporotics (EO). Exercising animals ran 4 h/wk for 1 yr. Two percent NH4Cl added to drinking water induced osteoporosis as shown by significantly lower femoral density and breaking strength and histomorphometrically quantified tibial trabecular bone volume but a normal mineral-to-matrix ratio in the O rats. The development of high-turnover osteoporosis in O rats was confirmed by significantly higher alkaline phosphatase activity (P less than 0.05), urinary hydroxyproline content (P less than 0.01), resorption surfaces (P less than 0.01), and histological parameters of bone formation (P less than 0.01). Exercise prevented all these biochemical, biophysical, and histological abnormalities in the EO group. Exercise had no influence on the density of normal femurs but tended to increase their breaking strength (by 11%) compared with femurs of C rats (P = 0.11).

Physiological characteristics of rugby players including muscle glycogen content and muscle fibre composition

There are few studies of the anthropomorphic and physiological characteristics of South African rugby players. Twenty-nine club rugby players were evaluated for body composition, maximal treadmill performance, muscle fibre composition and the muscle glycogen content, including the effects of carbohydrate-loading and playing a rugby match. The body composition and physiological characteristics of the players were similar to that previously reported for international players. Very high absolute values for maximum oxygen consumption (VO2 max) were measured in the forwards. Both backs and forwards had a preponderance of fast-twitch muscle fibres (57% and 53% respectively). Carbohydrate-loading increased pre-match muscle glycogen content but was unnecessary since severe muscle glycogen depletion did not occur during a match even in players on a normal mixed diet before competition. It is concluded that for forwards, a high absolute VO2 max, and for both backs and forwards a predominance of fast-twitch muscle fibres are pre-requisites for success in this sport. Pre-match carbohydrate-loading would appear to be necessary only when more than one match is to be played within 48 hours.

Factors Associated With Shin Soreness in Athletes

In brief: Twenty-five exercisers suffering from shin soreness were interviewed, examined, and monitored to identify factors associated with this injury. Twenty-five uninjured persons who matched the injured subjects in age, sex, and activities served as controls. Injured subjects had a greater range of subtalar joint motion and increased ankle dorsiflexion, reported a significantly lower calcium intake, had raised their training intensity before injury, and were using worn or poorly made shoes when injured. Factors not associated with injury included number of months subjects had participated in weight-bearing exercise, exercise surface, amount of stretching, height-weight ratio, and menstrual status. This study is the first to indicate a possible relationship between nutrition and shin soreness.