Hybrid muscle fibres co-expressing two or more myosin heavy chain (MHC) isoforms represent a significant proportion of fibres in many muscles, but the prevalence and precise composition of these fibres varies significantly among muscles and animal species. In the present study, we used a forced running protocol for 6 weeks to determine the effects of running exercise on the relative proportion of hybrid muscle fibre types in mouse muscles. In the course of this experiment, we also determined the relative proportions of these fibres in several different skeletal muscles, since data about hybrid fibres in the mouse are sparse. We found that the proportions of hybrid fibres in mouse muscles varied significantly among specific muscles (2-25%), but these proportions were unaffected by 6 weeks of forced running exercise. In contrast, weight-bearing muscles significantly increased in mass in response to running. These data suggest that hybrid muscle fibres are relatively refractory to the effects of moderate exercise and represent a stable phenotype in normal mouse muscles. The precise nature and physiological function of these fibres remain incompletely understood, but it is clear that hybrid fibres represent a common phenotype in many muscles.

All 3 biologics have similar efficacy in the treatment of CD when given as initial agents. Infliximab has a trend toward increased response after prior biologic failure; however, this did not meet statistical significance. Even after loss of response or failure of 2 previous biologics, trial of a third alternate biologic is an effective strategy.

Botulism toxin injection (BTI) is a well-known and relatively safe endoscopic treatment for achalasia. We report a case of a 90-year-old female diagnosed with achalasia who subsequently underwent BTI with symptomatic relief. The therapy was complicated by systemic botulism, however, leading to progressive muscle paralysis with diaphragmatic involvement requiring mechanical ventilation support. This is the first reported case of BTI for achalasia causing systemic botulism.

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