[Return to Sport (RTS) After Anterior Cruciate Ligament Reconstruction: Which Factors Influence the RTS Decision?] / Rückkehr zum Sport nach Rekonstruktion des vorderen Kreuzbandes ­ Welche Faktoren beeinflussen die Return to Sport-Entscheidung?

BACKGROUND: It is unknown which valid criteria should be considered to justify the decision for return to sport (RTS) following anterior cruciate ligament reconstruction (ACLR). The research question is whether gender, age, the outcome of the isokinetic maximal strength measurement and the single-leg hop test (quantitative/qualitative) influence the decision for RTS nine months after ACLR. METHODS: This study is a retrospective data analysis. The research question was evaluated with a multiple logistic regression analysis (MLR). The dependent variable, RTS yes/no, is based on the decision of the orthopaedist in charge of treatment nine months (±30 days) after ACLR. The following possible influencing factors were investigated: gender, age, limb symmetry index (LSI) of maximal knee extension and knee flexion strength at 60°/sec., LSI of single-leg hop test and evaluation of knee valgus. RESULTS: Data of 71 patients were included for MLR. The odds ratios (OR) for RTS increased with female gender (OR, 4.808; p=0.035), a higher LSI of maximal strength of knee extension (OR, 1.117; p=0.009) and a higher LSI of the single-leg hop test (OR, 1.125; p=0.020). Age, the LSI of maximal strength of knee flexion and knee valgus had no influence on the RTS decision. CONCLUSION: Gender and the limb symmetry indexes of the maximal strength of knee extension and of the single-leg hop test are associated with RTS nine months after ACLR. These results should be considered to optimise rehabilitation after ACLR.

Acute Effects of a Respiratory Sprint-Interval Session on Muscle Contractility.

INTRODUCTION: Respiratory muscle training has been shown to improve physical performance in healthy individuals and patients. One training modality for both inspiratory and expiratory muscles is respiratory muscle endurance training (RMET), which consists of normocapnic hyperpnea at constant ventilation for 30 min. Here, a new training regimen, respiratory muscle sprint-interval training (RMSIT), is introduced and tested for its potential to fatigue respiratory muscles. In addition, effects of both modalities on airway properties are investigated. METHODS: In 12 healthy subjects (six men and six women; 24 ± 3 yr; forced expiratory volume in 1 s, 115% ± 10%), changes in inspiratory transdiaphragmatic twitch pressure (Pdi,tw) and expiratory gastric twitch pressure (Pga,tw) were assessed during cervical magnetic stimulation or thoracic magnetic stimulation before and after a single bout of RMET and RMSIT. At similar time points, mechanical airway properties were assessed by impulse oscillometry. RMET was performed for 30 min at 60% of maximal voluntary ventilation, with constant tidal volume and breathing frequency. RMSIT consisted of six 30-s respiratory sprints (with 2-min breaks in between) at constant tidal volume, with the greatest possible breathing frequency and added resistance. RESULTS: Pdi,tw and Pga,tw decreased significantly after RMET (-17.7% ± 9.0% and -22.4% ± 18.5%; P < 0.01) and RMSIT (-18.1% ± 12.8% and -21.2% ± 13.1%; P < 0.01), and changes did not differ between training modalities (P = 0.50 and P = 0.12), suggesting similar levels of fatigue. Work of breathing per minute was 2.4 ± 0.8-fold greater in RMSIT than in RMET, whereas total work of breathing was substantially smaller in RMSIT (3.4 ± 0.8 kJ) than in RMET (15.0 ± 0.42 kJ). No subject showed clinically relevant changes in mechanical airway properties. CONCLUSIONS: Despite different work history, RMSIT appears to place a metabolic load on respiratory muscles similarly to RMET and could therefore be considered a time-saving and safe training alternative.

Aspects of respiratory muscle fatigue in a mountain ultramarathon race.

PURPOSE: Ultramarathon running offers a unique possibility to investigate the mechanisms contributing to the limitation of endurance performance. Investigations of locomotor muscle fatigue show that central fatigue is a major contributor to the loss of strength in the lower limbs after an ultramarathon. In addition, respiratory muscle fatigue is known to limit exercise performance, but only limited data are available on changes in respiratory muscle function after ultramarathon running and it is not known whether the observed impairment is caused by peripheral and/or central fatigue. METHODS: In 22 experienced ultra-trail runners, we assessed respiratory muscle strength, i.e., maximal voluntary inspiratory and expiratory pressures, mouth twitch pressure (n = 16), and voluntary activation (n = 16) using cervical magnetic stimulation, lung function, and maximal voluntary ventilation before and after a 110-km mountain ultramarathon with 5862 m of positive elevation gain. RESULTS: Both maximal voluntary inspiratory (-16% ± 13%) and expiratory pressures (-21% ± 14%) were significantly reduced after the race. Fatigue of inspiratory muscles likely resulted from substantial peripheral fatigue (reduction in mouth twitch pressure, -19% ± 15%; P < 0.01), as voluntary activation (-3% ± 6%, P = 0.09) only tended to be decreased, suggesting negligible or only mild levels of central fatigue. Forced vital capacity remained unchanged, whereas forced expiratory volume in 1 s, peak inspiratory and expiratory flow rates, and maximal voluntary ventilation were significantly reduced (P < 0.05). CONCLUSIONS: Ultraendurance running reduces respiratory muscle strength for inspiratory muscles shown to result from significant peripheral muscle fatigue with only little contribution of central fatigue. This is in contrast to findings in locomotor muscles. Whether this difference between muscle groups results from inherent neuromuscular differences, their specific pattern of loading or other reasons remain to be clarified.