Metabolic Demand of Paralympic Alpine Skiing in Sit-Skiing Athletes

Paralympic Alpine Skiing comprises three main categories, namely Standing, Visually Impaired and Sitting, to one of which athletes get classified depending on their individual impairment of ability. An existing sport profile of alpine skiing for able-bodied athletes facilitates the physical preparation process of Standing and Visually Impaired athletes. However, very little is known about performance determinants as well as content and structure of the physical preparation of athletes with congenital or acquired spinal cord injury competing in the Sitting class. The objective of this study was to describe the metabolic demands of Paralympic Alpine Skiing Sitting class athletes using laboratory and field measurements. The study determined maximal oxygen uptake (VO_2max), maximum heart rate (HR_max) and maximal blood lactate concentration ([La^-]) as well as ventilatory thresholds in laboratory testing (n = 6) as well as on-snow in Slalom (SL) carried out in a ski dome, and Giant-Slalom (GS) on a natural slope. On-snow test variables are expressed normalized to laboratory maximum values (%VO_2max, %HR_max). For SL, values reached ~30% VO_2max and ~60% HR_max whereas GS values were slightly higher reaching ~50% VO_2max and ~75% HR_max. Lactate concentration remained close to baseline values for SL and was slightly higher at ~3 mmol·L^-1 for GS. All athletes remained below their second ventilatory threshold and even skied for a long portion of runtime below their first ventilatory threshold. In general, measured metabolic values were lower than reported for able-bodied alpine skiers. However, despite the small and inhomogeneous sample covering all but one sit-skiing classes, strain of sit-skiing appears to be consistent throughout the five sit-skiing classes. Common measures of aerobic or anaerobic performance variables do not suggest further investigations in the field of metabolism for performance determinants in sit-skiing.

Key points

• Metabolic demand and strain of Paralympic sit-skiing is different to able-bodied skiing.
• Measured parameters of VO2max and [La-] are lower in sit-skiers compared to able-bodies skiers.
• Equipment used for sit-skiing is suggested to absorb external forces to some degree, thereby lowering the strain.
• Implications for training focus (e.g. skiing higher volumes with a focus on technique) and the physical conditioning process (aerobic/ anaerobic capacity are suggested to be no performance determinants) may be derived.

Key words: Paralympic winter sports, paraplegia, wheelchair exercise physiology     

WhatSAP — 2B4 sends mixed messages in the absence of SAP

2B4 (CD244), a member of the SLAM‐related receptor family, has important immuno‐regulatory functions including coactivating the cytotoxicity and cytokine secretion of NK cells. Immune modulation by 2B4 is dependent on the small intracellular signaling molecule SAP. In patients suffering from X‐linked lymphoproliferative disease (XLP1), SAP is nonfunctional, not only abolishing the activating function of 2B4, but rendering this receptor inhibitory. In this issue of European Journal of Immunology, Meazza et al. [Eur. J. Immunol. 2014. 44: 1526–1534.] demonstrate that 2B4‐mediated inhibition in NK cells from XLP1 patients is selective. While the activation of NK cells via ITAM‐based receptors is blocked by inhibitory 2B4, DNAM‐1, and NKG2D‐dependent NK‐cell activation is not affected by SAP deficiency. These findings provide an important insight into the different defective NK‐cell functions in XLP1 patients and demonstrate the differential integration of redundant receptor signaling pathways in NK cells.     

From the Cover: Staphylococcus aureus secretes a unique class of neutrophil serine protease inhibitors

Neutrophils are indispensable for clearing infections with the prominent human pathogen Staphylococcus aureus. Here, we report that S. aureus secretes a family of proteins that potently inhibits the activity of neutrophil serine proteases (NSPs): neutrophil elastase (NE), proteinase 3, and cathepsin G. The NSPs, but not related serine proteases, are specifically blocked by the extracellular adherence protein (Eap) and the functionally orphan Eap homologs EapH1 and EapH2, with inhibitory-constant values in the low-nanomolar range. Eap proteins are together essential for NSP inhibition by S. aureus in vitro and promote staphylococcal infection in vivo. The crystal structure of the EapH1/NE complex showed that Eap molecules constitute a unique class of noncovalent protease inhibitors that occlude the catalytic cleft of NSPs. These findings increase our insights into the complex pathogenesis of S. aureus infections and create opportunities to design novel treatment strategies for inflammatory conditions related to excessive NSP activity.Infections with the human pathogen Staphylococcus aureus constitute a major risk to human health. Although this bacterium harmlessly colonizes more than 30% of the population via the nose or skin, it causes severe morbidity and mortality upon invasion of deeper tissues (1). To avert these serious infections, neutrophils play an indispensable role (2). Neutrophil serine proteases (NSPs), including neutrophil elastase (NE), proteinase 3 (PR3), and cathepsin G (CG), are important for various neutrophil functions. Active NSPs are stored within the azurophilic granules (3), but upon neutrophil activation, they either enter the nucleus to regulate extracellular trap (NET) formation (4) or they are released into the extracellular milieu to kill certain bacteria (5), cleave bacterial virulence factors (5, 6), or regulate immune responses by cleaving chemokines and receptors (7). Recently, a fourth neutrophil serine protease, denoted NSP4, was identified (8).Given the central role of NSPs in neutrophil function, we wondered whether S. aureus had evolved mechanisms to cope with NSPs. In this study, we discover that S. aureus secretes a family of proteins that specifically and potently block NSPs: extracellular adherence protein (Eap) and the hitherto functional orphans Eap-homologue (EapH) 1 and 2. Structural studies presented here show that Eap molecules represent a unique class of noncovalent NSP inhibitors that is distinct from the well-known chelonianin class of inhibitors. These mechanistic insights can initiate development of novel, broad-range NSP inhibitors to be used in various inflammatory conditions. Furthermore, these insights increase our understanding of the pathogenicity of S. aureus and underline the exceptional capability of this pathogen to adapt to its host by modulating the immune response.