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Lisano, JK, Smith, JD, Mathias, AB, Christensen, M, Smoak, P, Phillips, KT, Quinn, CJ, and Stewart, LK. Performance and health-related characteristics of physically active men using marijuana. J Strength Cond Res 33(6): 1659-1669, 2019-The influence of chronic marijuana use on the performance and health of physically active individuals has yet to be fully elucidated. The purpose of this study was to explore pulmonary function, aerobic and anaerobic fitness, strength, serum testosterone, cortisol, C-reactive protein (CRP), Δ-9-tetrahydrocannabinol (THC), 11-nor-9-carboxy-Δ-9-tetrahydrocannabinol (THC-COOH), and 11-hydroxy-Δ-9-tetrahydrocannabinol (THC-OH) concentrations in a physically active population either using or not using marijuana. Healthy, physically active males (N = 24) were compared based on their marijuana-use status: marijuana users (MU; n = 12) and nonusers (NU; n = 12). Statistical analysis (p = 0.05) revealed no difference between groups for age, body mass, body mass index, body fat, forced expiratory volume in 1 second percentage, VO2max, anaerobic power output, strength measures, testosterone, or cortisol concentrations. Although not statistically significant, MU showed a trend to fatigue to a greater percentage of absolute power output than NU from the beginning to the end of the Wingate Anaerobic Power Assessment (p = 0.08, effect size = 0.75). C-reactive protein in MU (1.76 ± 2.81 mg·L) and NU (0.86 ± 1.49 mg·L) was not significantly different (p = 0.60) but placed MU at moderate risk and NU at low risk for cardiovascular disease. Anaerobic fatigue was the only performance variable to show a trend for difference between groups. These results suggest that marijuana use in physically active males may not have significant effects on performance; however, it may be linked to elevated concentrations of CRP which place users at a higher risk for cardiovascular disease.

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BACKGROUND: The skeletal muscle toxicity that accompanies the chemotherapy drug doxorubicin (DOX) may lead to cancer patient weakness and fatigue. This myotoxicity involves myogenic regulatory factor (MRF) disruption which alters muscle integrity and regeneration. Endurance exercise enhances MRF expression and thereby may mitigate DOX-induced MRF disruptions. This study examined the effects of endurance training and DOX treatment on myogenic regulatory factor (MRF) expression. METHODS: Male rats were exercise trained (EXER) or remained sedentary (SED) for two weeks. EXER and SED then received either DOX (15 mg/kg) or saline (SAL). Soleus, extensor digitorum longus (EDL), and diaphragm were excised 24 hours post injection, and MRF expression was analyzed. RESULTS: Significant Myf5 drug and activity effects were observed in the soleus with EXER+DOX expressing higher Myf5 than SED+DOX. A significant drug effect was detected in soleus MyoD, and a significant activity effect was detected in soleus Mrf4. No main effects or interactions were observed in the EDL, but in the diaphragm, a significant activity effect was observed for Myf5 with EXER+DOX expressing higher levels than SED+DOX. CONCLUSION: Doxorubicin treatment increased soleus MRFs and exercise boosted MRF response in soleus and diaphragm suggesting that exercise may enhance regenerative signaling with DOX treatment. LEVEL OF EVIDENCE: I b, individual randomized controlled trial.

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INTRODUCTION: Chemotherapy treatment with doxorubicin (DOX) can have a negative effect on normal skeletal muscle function. Recent research demonstrates the potential value of exercise in alleviating DOX-induced cardiotoxicity. Yet up to now, little research has been done to examine whether exercise might also be effective in addressing DOX's skeletal muscle adverse effects, especially because posttreatment skeletal muscle dysfunction may cause patient difficulties with completing activities of daily living. The main aim of this study was to examine how resistance training (RT) and treadmill (TM) training play a role in preventing DOX-induced skeletal muscle dysfunction. METHODS: Male Sprague-Dawley rats were randomly placed into an RT, TM, or sedentary (SED) group for 10 wk and then received either a bolus injection of DOX (15 mg·kg) or saline as a control. Skeletal muscle function was then assessed ex vivo 5 d after injection. RESULTS: SED animals treated with DOX showed significantly lower maximal twitch force, maximal rate of force production, and maximal rate of force decline versus SED + saline in the soleus (SOL) (Type I muscle). In the extensor digitorum longus (Type II muscle), treatment with DOX resulted in a significantly lower maximal rate of force production and maximal rate of force decline. RT preserved maximal twitch force and maximal rate of force decline in the SOL. TM attenuated DOX-induced fatigue in the SOL but not in the extensor digitorum longus. CONCLUSION: These findings suggest that RT and TM before DOX could be useful in preserving skeletal muscle function and minimizing fatigue after chemotherapy, but this protection may be dependent on the skeletal muscle type.

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The use of prior exercise training has shown promise in minimizing doxorubicin (DOX)-induced physical impairments. The purpose of this study was to compare changes in thymus mass, thymocyte (T-cell) number, and tissue peroxidation following chronic endurance exercise and DOX treatment in the rat. The thymus mass, number of viable T-cells, and levels of malondialdehyde and 4-hydroxyalkenals (MDA+4-HAE) were compared 3 days post-injection between rats assigned to the following treatment conditions: (a) 10 weeks of endurance training, followed by a saline injection 24 hours after the last training session (TM+SAL); (b) treadmill training as above, followed by a single, bolus 10-mg/kg injection of DOX (TM+10); (c) treadmill training with 12.5 mg/kg of DOX (TM+12.5); (d) sedentary (without exercise) and a saline injection (SED+SAL); (e) sedentary with 10 mg/kg of DOX (SED+10); and (f) sedentary with 12.5 mg/kg (SED+12.5). Thymic mass and T-cell numbers significantly decreased following DOX injections. TM rats exhibited significantly less lipid peroxidation compared with paired-dose SED groups. TM+10 did not significantly differ from SED+SAL in thymic levels of lipid peroxidation. We conclude that chronic endurance exercise decreases levels of lipid peroxidation in the thymus seen with acute DOX treatment.

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1. Doxorubicin (DOX) is a highly effective and commonly used anthracycline antibiotic used to treat cancer patients. The side effects of DOX are manifested in a more delayed manner in children and multidrug resistant proteins (MRPs) may factor into this phenomenon. MRPs are known to extrude DOX and may factor into the degree of cardiac DOX accumulation. 2. The purpose of this study was to examine age-related differences in muscle MRP expression and DOX accumulation. 3. Female Sprague-Dawley rats were randomly selected to receive a 15-mg DOX/kg body weight bolus injection (i.p.) at various ages. 4. Cardiac and extensor digitorum longus DOX accumulation was markedly increased as animals aged from 4 to 24 weeks. In contrast, no differences in soleus accumulation were observed. A significant age-related reduction in MRP-2 and MRP-7 expression was detected in cardiac and extensor digitorum longus tissues with no age differences in MRP-1 expression in any tissues analyzed. MRP-6 was not detected in any tissues. 5. These data suggest that aging is associated with increased DOX accumulation and an age-related decrease in MRP expression may be a factor.

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