Ibuprofen before Exercise Does Not Prevent Cortical Bone Adaptations to Training

Acetaminophen influences musculoskeletal signaling but not adaptations to endurance exercise training

Acetaminophen (ACE) is a widely used analgesic and antipyretic drug with various applications, from pain relief to fever reduction. Recent studies have reported equivocal effects of habitual ACE intake on exercise performance, muscle growth, and risks to bone health. Thus, this study aimed to assess the impact of a 6-week, low-dose ACE regimen on muscle and bone adaptations in exercising and non-exercising rats. Nine-week-old Wistar rats (n = 40) were randomized to an exercise or control (no exercise) condition with ACE or without (placebo). For the exercise condition, rats ran 5 days per week for 6 weeks at a 5% incline for 2 min at 15 cm/s, 2 min at 20 cm/s, and 26 min at 25 cm/s. A human equivalent dose of ACE was administered (379 mg/kg body weight) in drinking water and adjusted each week based on body weight. Food, water intake, and body weight were measured daily. At the beginning of week 6, animals in the exercise group completed a maximal treadmill test. At the end of week 6, rats were euthanized, and muscle cross-sectional area (CSA), fiber type, and signaling pathways were measured. Additionally, three-point bending and microcomputer tomography were measured in the femur. Follow-up experiments in human primary muscle cells were used to explore supra-physiological effects of ACE. Data were analyzed using a two-way ANOVA for treatment (ACE or placebo) and condition (exercise or non-exercise) for all animal outcomes. Data for cell culture experiments were analyzed via ANOVA. If omnibus significance was found in either ANOVA, a post hoc analysis was completed, and a Tukey's adjustment was used. ACE did not alter body weight, water intake, food intake, or treadmill performance (p > .05). There was a treatment-by-condition effect for Young's Modulus where placebo exercise was significantly lower than placebo control (p < .05). There was no treatment by condition effects for microCT measures, muscle CSA, fiber type, or mRNA expression. Phosphorylated-AMPK was significantly increased with exercise (p < .05) and this was attenuated with ACE treatment. Furthermore, phospho-4EBP1 was depressed in the exercise group compared to the control (p < .05) and increased in the ACE control and ACE exercise group compared to placebo exercise (p < .05). A low dose of ACE did not influence chronic musculoskeletal adaptations in exercising rodents but acutely attenuated AMPK phosphorylation and 4EBP1 dephosphorylation post-exercise.

Sex differences in the effect of diet, obesity, and exercise on bone quality and fracture toughness

Bone fragility and obesity are both diseases that are multifactorial in etiology and pathology. The contributing role of high fat diet (HFD) versus energy overconsumption on bone health is controversial. Exercise is often prescribed for improving bone health, but it is unclear whether HFD or overconsumption influences skeletal adaptations to exercise. Female and male Wistar rats were fed HFD or low fat diet (LFD) for 10 weeks, starting at 8 weeks of age. Within HFD, rats were labeled Obesity-Resistant (OR) or Obesity-Prone (OP) based on weight and fat gain. Within each diet and phenotype group, rats were randomized to treadmill exercise or sedentary control (SED) for the final 4 weeks. Femurs were assessed for fracture toughness. Cortical lamellar and nonlamellar bone microscale material behavior and chemistry were assessed using nanoindentation and Raman spectroscopy. Female bones had higher fracture toughness and mineral: matrix ratio than male bones. Diet and energy overconsumption affected bone characteristics in a sex-dependent manner, where the divergence between OP and OR in response to HFD occurred more rapidly in males. Diet composition, in general, had a stronger effect on bone quality than overconsumption. HFD dramatically decreased bone size and lamellar mineral:matrix compared to LFD. Effects of short-term exercise training on microscale tissue properties were generally more robust with LFD. Exercise enhanced the contrast between lamellar and nonlamellar bone for nanoindentation modulus but decreased this contrast for plastic work. Our data demonstrate the complexities in the relationship between diet and obesity and highlight the importance of addressing both aspects when characterizing bone quality and fracture resistance.

Emerging evidence that adaptive bone formation inhibition by non-steroidal anti-inflammatory drugs increases stress fracture risk

There is mounting evidence suggesting that the commonly used analgesics, non-steroidal anti-inflammatory drugs (NSAIDs), may inhibit new bone formation with physical training and increase risk of stress fractures in physically active populations. Stress fractures are thought to occur when bones are subjected to repetitive mechanical loading, which can lead to a cycle of tissue microdamage, repair, and continued mechanical loading until fracture. Adaptive bone formation, particularly on the periosteal surface of long bones, is a concurrent adaptive response of bone to heightened mechanical loading that can improve the fatigue resistance of the skeletal structure, and therefore may play a critical role in offsetting the risk of stress fracture. Reports from animal studies suggest that NSAID administration may suppress this important adaptive response to mechanical loading. These observations have implications for populations such as endurance athletes and military recruits who are at risk of stress fracture and whose use of NSAIDs is widespread. However, results from human trials evaluating exercise and bone adaptation with NSAID consumption have been less conclusive. In this review, we identify knowledge gaps that must be addressed to further support NSAID-related guidelines intended for at-risk populations and individuals.

Impact of Exercise and Activity on Weight Regain and Musculoskeletal Health Post-Ovariectomy

The purpose of this study was to determine whether obesity and/or exercise training alters weight regain and musculoskeletal health after ovariectomy (OVX). Female rats were fed high-fat diet (HFD) to reveal obesity-prone (OP) and obesity-resistant (OR) phenotypes. The OP and OR exercising (EX) and sedentary (SED) rats were calorically restricted to lose 15% of body weight using medium-fat diet. Rats were then maintained in energy balance for 8 wk before OVX. After OVX and a brief calorically limited phase, rats were allowed to eat ad libitum until body weight plateaued. Starting at weight loss, EX ran 1 h·d, 6 d·wk, 15 m·min. Energy intake, spontaneous physical activity (SPA), and total energy expenditure were evaluated at the end of weight maintenance pre-OVX, and at three time points post-OVX: before weight regain, during early regain, and after regain. Data are presented as mean ± SE. Exercise attenuated weight regain after OVX in OP only (OP-EX, 123 ± 10 g; OP-SED, 165 ± 12 g; OR-EX, 121 ± 6 g; OR-SED, 116 ± 6 g), which was primarily an attenuation of fat gain. The early post-OVX increase in energy intake explained much of the weight regain, and was similar across groups. Exercising improved bone strength, as did maintaining SPA. Group differences in muscle mitochondrial respiration were not significant. The large decrease in SPA due to OVX was persistent, but early weight regain was dependent on decreased SPA. In conclusion, leanness and exercise do not necessarily protect from OVX-induced weight gain. Exercise prevented weight gain in obese rats, but loss of SPA was the greatest contributor to post-OVX weight gain. Thus, understanding the mechanisms resulting in reduction in SPA after ovarian hormone loss is critical in the prevention of menopause-associated metabolic dysfunction.