Stephen Grinton

High intensity training-induced changes in skeletal muscle antioxidant enzyme activity

These experiments tested the hypothesis that high intensity (interval) training is superior to moderate intensity (continuous) exercise training in the upregulation of antioxidant enzyme activity in skeletal muscle. To test this postulate, we examined changes in oxidative and antioxidant enzyme activities in rat skeletal muscle following 12 wk of either interval (6 x approximately 5-min intervals at approximately 80-95% VO2max) or continuous (45 min at approximately 70% VO2max) exercise training. Both continuous and interval training resulted in significantly elevated (P < 0.05) succinate dehydrogenase (SDH) and 3-hydroxyacyl-CoA-dehydrogenase (HADH) activities in the gastrocnemius (G) and soleus (S) muscles compared with controls. SDH and HADH activities in the G and S muscles did not differ between the two exercise groups. Glutathione peroxidase (GPX) activity exceeded controls (P < 0.05) in only the interval trained S muscle. Soleus superoxide dismutase (SOD) activity was higher (P < 0.05) in both exercise groups compared with controls. No differences in SOD activity existed between interval and continuous trained animals. We conclude that when matched for oxygen cost, interval and continuous exercise training result in similar increases in SOD activity. However, high intensity interval exercise is superior to moderate intensity continuous exercise in the promotion of GPX activity in the S.

Incidence of exercise induced hypoxemia in elite endurance athletes at sea level

SummaryRecent evidence suggests that exercise-induced hypoxemia (EIH) may occur in healthy trained endurance athletes. However, at present, no data exist to describe the regularity of EIH in athletes or non-athletes. Therefore, the purpose of the present investigation was to determine the incidence of EIH during exercise in healthy subjects varying in physical fitness. Subjects (N=68) performed an incremental cycle ergometer test to volitional fatigue with percent arterial oxyhemoglobin saturation (%SaO2) measured min-by-min. For the purpose of data analysis subjects were divided into three groups according to their level of physical training: 1) untrained (N=16), 2) moderately trained (N=27), and 3) elite highly trained endurance athletes (N=25). EIH was defined as a %SaO2 of ≤91% during exercise. EIH did not occur in any of the untrained subjects or the moderately trained subjects. However, EIH occurred in 52% of the highly trained endurance athletes tested and was highly reproducible (r=0.95; P<0.05). These findings further confirm the existence of EIH in healthy highly trained endurance athletes and suggests a rather high incidence of EIH in this healthy population. Hence, it is important that the clinician or physiologist performing exercise testing in elite endurance athletes recognize that EIH can and does occur in the elite endurance athlete in the absence of lung disease.

High intensity exercise training-induced metabolic alterations in respiratory muscles.

Limited information exists concerning the effects of high intensity interval exercise training (HIET) on metabolic alterations in both inspiratory and expiratory muscles. To test the hypothesis that HIET will improve the oxidative capacity of the diaphragm and major expiratory muscles, we examined Krebs cycle and beta oxidation enzyme activities in the diaphragm and three groups of expiratory (abdominal) muscles in rats subjected to 12 weeks (5 days.wk-1) of treadmill exercise. Two groups of female Sprague-Dawley rats (age ca 120 days) were studied: (1) HIET group (n = 10; animals performed 6 x ca 5-min running intervals.day-1 at ca 90-95% VO2max); (2) sedentary control group (n = 7). When compared to controls, HIET resulted in significantly elevated (P less than 0.05) activities of 3-hydroxy-acyl-Co-A dehydrogenase (HADH) and citrate synthase (CS) in the costal diaphragm, rectus abdominus, external obliques, and the plantaris muscles. In contrast, training did not increase (P greater than 0.05) the activities of CS or HADH in the crural diaphragm or the internal obliques/transversus abdominus muscles. By comparison, the training-induced increases in oxidative capacity (e.g., CS activity) in the costal diaphragm, rectus abdominus, and external obliques were relatively small (ca 23, 10, 12%, respectively) when contrasted to the exercise-induced increase in CS activity in the plantaris muscle (ca 47%). We conclude that HIET results in small but significant improvements in the oxidative and beta oxidation capacities of the costal diaphragm and at least two abdominal expiratory muscles.

Endurance training-induced increases in expiratory muscle oxidative capacity.

Recent evidence demonstrates that endurance exercise training improves the oxidative capacity of the major mammalian inspiratory muscle (e.g., costal diaphragm). In contrast, no data exist concerning the effects of exercise training on abdominal expiratory muscles. We tested the hypothesis that 12 wk of endurance exercise training would significantly increase the activity of selected beta oxidation and Krebs cycle enzymes of abdominal expiratory muscles of the rat. To test this hypothesis two groups of female Sprague-Dawley rats were studied: group 1, continuous exercise training (n = 13); and group 2, sedentary control (n = 6). Exercise trained animals ran 5 d.wk-1 on a motorized treadmill for 45 min.d-1 at approximately 75-80% VO2max. When compared with controls, exercise training resulted in elevated (P less than 0.05) activities of 3-hydroxy-acyl-Co-A dehydrogenase (HADH) and citrate synthase (CS) in two abdominal expiratory muscles (rectus abdominus and external obliques). In contrast, training did not alter (P greater than 0.05) CS or HADH activity in the internal obliques/transversus abdominus muscles. In general, the training-induced increases in expiratory muscles CS activity were relatively small (approximately 10-13%) when compared with the training-induced increase in CS activity in the plantaris muscle (approximately 44%). These data demonstrate that continuous exercise training results in small but statistically significant improvements in the oxidative and beta oxidation capacities of expiratory muscles.

Quiescent left atrial myxoma

Copyright ,c’ 1994 by Mosby-Year Book, Inc. 0002.8703/94/

Quality control in exercise testing

3.00 + 0 4/4/63613 has not appreciably enhanced the understanding of the natural history of this disorder. The potentially sudden, devastating nature of the complications of this tumor mandates prompt surgical excision once the diagnosis is made.4 The documentation of the growth rate of myxoma has been limited primarily to observation of recurrent tumors after a prior excision.5 Recently, it has been suggested that primary intracardiac myxomas grow at a rapid rate.6-8 We report a patient who had documentation of a left atrial myxoma by echocardiography over an interval of more than 2 years. A 72-year-old man presented for general examination at the Mayo Clinic in July 1992. He was free of symptoms except for a mild resting tremor, which had been present for several years. His medical history was remarkable for benign colon polyps and prostate cancer, diagnosed in 1989, for which he received radiotherapy. He also gave a history of an abnormal echocardiogram performed in March 1990 as part of a general examination by another physician, which he reported showed evidence of a possible left atria1

Endurance-training-induced cellular adaptations in respiratory muscles

Cardiopulmonary exercise testing is a technically demanding procedure. Most current testing systems are self-contained and can be configured to allow relatively little operator interface during the procedure. Internal quality control procedures are convenient but limited. In a busy laboratory, one can rely too heavily on the internal quality control software and not critically evaluate the actual data. In this paper, we will discuss potential errors in exercise testing and offer suggestions to avoid them. Because manufacturers are continually introducing new models and improving old ones, we have not compared specific exercise testing systems. We advise laboratory directors and technical personnel to schedule time for regular routine quality control checks and evaluation of the quality of exercise testing data.