Blood flow restriction training does not negatively alter the mechanical strength or histomorphology of uninjured equine superficial digital flexor tendons.

BACKGROUND: Low load exercise training with blood flow restriction (BFR) has become increasingly used by human physical therapists to prescribe controlled exercise following orthopaedic injury; its effects on the equine superficial digital flexor tendon (SDFT), however, are unknown. OBJECTIVE: To investigate outcomes of pressure specific BFR walking exercise on uninjured equine SDFT biomechanics and histomorphology. STUDY DESIGN: Controlled in vivo experiment. METHODS: Four forelimbs of four horses were exposed to 40 BFR-walk sessions (10-min interval walking) on a treadmill over a 56-day study period with their contralateral forelimbs serving as untreated controls. Similarly, four forelimbs of four control horses were exposed to 40 sham cuff walk sessions. On study Day 56, all horses (n = 8) were humanely euthanised and forelimb SDFTs underwent non-destructive biomechanical testing and corresponding histomorphological analysis. Significance in biomechanical parameters between treatment groups was analysed using a mixed-effects ANOVA with Tukey's post-hoc tests. RESULTS: Statistically significant differences in SDFT stiffness for both first (p = 0.02) and last cycles (p = 0.03) were appreciated within the BFR treated group only, with BFR exposed forelimbs being significantly stiffer than the contralateral unexposed forelimbs. When normalised to cross-sectional area, no significant differences were appreciated among treatment groups in elastic modulus for the first (p = 0.5) or last cycles (p = 0.4). No histological differences were appreciated among treatment groups according to Bonar, Movin, or musculotendinous junction evaluation criteria. MAIN LIMITATIONS: Short-term comparisons were performed in a small sample population without correlation to performance outcome measures. Optimal occlusion percentages and walk protocols remain unknown. CONCLUSIONS: This study demonstrated no negative impact of BFR on mechanical strength of the equine SDFT; however, evidence suggests that BFR results in increased tendon stiffness based on biomechanical testing and subsequent calculations. No consistent detrimental histomorphological changes were seen.

CONTEXTO: Exercício de baixa carga com restrição do fluxo sanguíneo (RFS) tem sido cada vez mais utilizado por fisioterapeutas humanos para tratar lesões ortopédicas. Porém, seus efeitos no tendão flexor digital superficial (TFDS) de equinos não é conhecida. OBJETIVOS: O objetivo deste estudo foi investigar o efeito de específicas pressões com RFS durante o passo em cavalos sem lesão no TFDS, por meio de histologia e análise biomecânica. DELINEAMENTO DO ESTUDO: Estudo controlado. MÉTODOS: Quatro membros torácicos de quatro cavalos foram expostos a 40 sessões de RFS durante o passo (10 minutos de caminhada intervalada), ao longo de 56 dias. O membro contralateral foi utilizado como controle. Da mesma forma, quatro membros de quatro cavalos controle foram expostos a 40 sessões simuladas de caminhada com torniquete. No dia 56, todos os cavalos (n = 8) foram eutanasiados, e os TFDS foram submetidos a testes biomecânicos não destrutivos e análise histológica. A significância dos parâmetros biomecânicos entre tratamentos foi analisada utilizando ANOVA de efeitos mistos, seguida pelo teste de Tukey. RESULTADOS: A rigidez do TFDS foi estatisticamente diferente nos primeiros (p = 0.02) e últimos (p = 0.03) ciclos no grupo submetido à RFS, sendo os membros tratados significativamente mais rígidos do que os membros contralaterais não expostos ao tratamento. Quando normalizado para a área transversal, não foi observada diferença significativa entre os grupos de tratamento no módulo de elasticidade para os primeiros (p = 0.5) e últimos (p = 0.4) ciclos. Não foram identificadas diferenças histológicas nos diferentes tipos de tratamento, de acordo com os critérios de avaliação Bonar, Movin e de junção musculo­tendínea. PRINCIPAIS LIMITAÇÕES: Comparações de curto prazo foram realizadas em uma amostra pequena da população, sem correlação com medidas de resultados de desempenho. As porcentagens ideais de oclusão e os protocolos de caminhada permanecem desconhecidos. CONCLUSÕES: Este estudo não demonstrou impacto negativo do RFS na resistência mecânica do TFDS equino; no entanto, as evidências sugerem que a RFS resulta em aumento da rigidez do tendão com base em testes biomecânicos e cálculos subsequentes. Nenhuma alteração histológica prejudicial consistente foi observada.

Phytochemical compound PB125 attenuates skeletal muscle mitochondrial dysfunction and impaired proteostasis in a model of musculoskeletal decline.

Impaired mitochondrial function and disrupted proteostasis contribute to musculoskeletal dysfunction. However, few interventions simultaneously target these two drivers to prevent musculoskeletal decline. Nuclear factor erythroid 2-related factor 2 (Nrf2) activates a transcriptional programme promoting cytoprotection, metabolism, and proteostasis. We hypothesized daily treatment with a purported Nrf2 activator, PB125, in Hartley guinea pigs, a model of musculoskeletal decline, would attenuate the progression of skeletal muscle mitochondrial dysfunction and impaired proteostasis and preserve musculoskeletal function. We treated 2- and 5-month-old male and female Hartley guinea pigs for 3 and 10 months, respectively, with the phytochemical compound PB125. Longitudinal assessments of voluntary mobility were measured using Any-MazeTM open-field enclosure monitoring. Cumulative skeletal muscle protein synthesis rates were measured using deuterium oxide over the final 30 days of treatment. Mitochondrial oxygen consumption in soleus muscles was measured using high resolution respirometry. In both sexes, PB125 (1) increased electron transfer system capacity; (2) attenuated the disease/age-related decline in coupled and uncoupled mitochondrial respiration; and (3) attenuated declines in protein synthesis in the myofibrillar, mitochondrial and cytosolic subfractions of the soleus. These effects were not associated with statistically significant prolonged maintenance of voluntary mobility in guinea pigs. Collectively, treatment with PB125 contributed to maintenance of skeletal muscle mitochondrial respiration and proteostasis in a pre-clinical model of musculoskeletal decline. Further investigation is necessary to determine if these documented effects of PB125 are also accompanied by slowed progression of other aspects of musculoskeletal dysfunction. KEY POINTS: Aside from exercise, there are no effective interventions for musculoskeletal decline, which begins in the fifth decade of life and contributes to disability and cardiometabolic diseases. Targeting both mitochondrial dysfunction and impaired protein homeostasis (proteostasis), which contribute to the age and disease process, may mitigate the progressive decline in overall musculoskeletal function (e.g. gait, strength). A potential intervention to target disease drivers is to stimulate nuclear factor erythroid 2-related factor 2 (Nrf2) activation, which leads to the transcription of genes responsible for redox homeostasis, proteome maintenance and mitochondrial energetics. Here, we tested a purported phytochemical Nrf2 activator, PB125, to improve mitochondrial function and proteostasis in male and female Hartley guinea pigs, which are a model for musculoskeletal ageing. PB125 improved mitochondrial respiration and attenuated disease- and age-related declines in skeletal muscle protein synthesis, a component of proteostasis, in both male and female Hartley guinea pigs.