Unlocking the depths: multiple factors contribute to risk for hypoxic blackout during deep freediving

PURPOSE

To examine the effect of freediving depth on risk for hypoxic blackout by recording arterial oxygen saturation (SpO2) and heart rate (HR) during deep and shallow dives in the sea.

METHODS

Fourteen competitive freedivers conducted open-water training dives wearing a water-/pressure proof pulse oximeter continuously recording HR and SpO2. Dives were divided into deep (> 35 m) and shallow (10-25 m) post-hoc and data from one deep and one shallow dive from 10 divers were compared.

RESULTS

Mean ± SD depth was 53 ± 14 m for deep and 17 ± 4 m for shallow dives. Respective dive durations (120 ± 18 s and 116 ± 43 s) did not differ. Deep dives resulted in lower minimum SpO2 (58 ± 17%) compared with shallow dives (74 ± 17%; P = 0.029). Overall diving HR was 7 bpm higher in deep dives (P = 0.002) although minimum HR was similar in both types of dives (39 bpm). Three divers desaturated early at depth, of which two exhibited severe hypoxia (SpO2 ≤ 65%) upon resurfacing. Additionally, four divers developed severe hypoxia after dives.

CONCLUSIONS

Despite similar dive durations, oxygen desaturation was greater during deep dives, confirming increased risk of hypoxic blackout with increased depth. In addition to the rapid drop in alveolar pressure and oxygen uptake during ascent, several other risk factors associated with deep freediving were identified, including higher swimming effort and oxygen consumption, a compromised diving response, an autonomic conflict possibly causing arrhythmias, and compromised oxygen uptake at depth by lung compression possibly leading to atelectasis or pulmonary edema in some individuals. Individuals with elevated risk could likely be identified using wearable technology.

Rifle carriage affects gear distribution during on-snow skiing in female and male biathletes

The aim was to investigate whether rifle carriage affects gear distribution during on-snow skiing in highly-trained biathletes, and whether there were any associated sex differences. Twenty-eight biathletes (11 women, 17 men) skied a 2230-m lap at competition speed twice, one lap with the rifle (WR) and the other lap without the rifle (NR). The biathletes wore a portable 3D-motion analysis system while skiing, which enabled characterisation of distance and time in different gears. Skiing WR increased lap time compared to NR (412 (90) vs. 395 (91) s, p < 0.001). The biathletes used gear 2 to a greater extent WR compared to NR (distance: 413 ± 139 vs. 365 ± 142 m; time: 133 (95) vs. 113 (86) s; both p < 0.001) and gear 3 less (distance: 713 ± 166 vs. 769 ± 182 m, p < 0.001; time: 141 ± 33 vs. 149 ± 37 s, p = 0.008), with similar patterns for women and men. Differences between WR and NR in the use of gears 3 and 2 were more extensive for moderate compared to steeper uphill terrain. Rifle carriage increased the use of gear 2, which was negatively associated with performance. Therefore, preparing biathletes to be able to cover more distance in gear 3 WR, especially in moderate uphill terrain, may improve biathlon skiing performance.

The Effect of Match Schedule on Accelerometry-Derived Exercise Dose during Training Sessions throughout a Competitive Basketball Season

Accelerometry-derived exercise dose (intensity × duration) was assessed throughout a competitive basketball season. Nine elite basketballers wore accelerometers during a Yo-Yo intermittent recovery test (Yo-Yo-IR1) and during three two-week blocks of training that represented phases of the season defined as easy, medium, and hard based on difficulty of match schedule. Exercise dose was determined using accumulated impulse (accelerometry-derived average net force × duration). Relative exercise intensity was quantified using linear relationships between average net force and oxygen consumption during the Yo-Yo-IR1. Time spent in different intensity zones was computed. Influences of match schedule difficulty and playing position were evaluated. Exercise dose reduced for recovery and pre-match tapering sessions during the medium match schedule. Exercise dose did not vary during the hard match schedule. Exercise dose was not different between playing positions. The majority of activity during training was spent performing sedentary behaviour or very light intensity activity (64.3 ± 6.1%). Front-court players performed a greater proportion of very light intensity activity (mean difference: 6.8 ± 2.8%), whereas back-court players performed more supramaximal intensity activity (mean difference: 4.5 ± 1.0%). No positional differences existed in the proportion of time in all other intensity zones. Objective evaluation of exercise dose might allow coaches to better prescribe and monitor the demands of basketball training.

Accelerometry-Derived Relative Exercise Intensities in Elite Women's Basketball

This study assessed accelerometry-derived relative exercise intensity during elite women's basketball match play. The influence of player position/role and match period on relative exercise intensities was evaluated. Ten basketballers wore accelerometers during a Yo-Yo intermittent recovery test (Yo-Yo-IR1) and 18 competitive matches. Relative exercise intensity was quantified using predicted oxygen consumption reserve determined using correlations from Yo-Yo-IR1. Total time, bout frequency and bout duration were calculated in seven intensity zones and compared between quarters, positions (back-court vs. front-court) and roles (starters vs. bench). Back-court players spent 6.0±1.9% more match time performing supramaximal activity when compared to front-court players (p<0.045). Back-court players experienced more supramaximal bouts (125±37 vs. 52±36; p=0.031) of greater average duration (2.1±0.4 vs. 1.4±0.2 s; p=0.021) and maximum duration (7±2 vs. 3±1 s; p=0.020). More sedentary to very light activity was observed in the 2^nd and 4^th quarters compared to the 1^st and 3^rd quarters (p<0.05). Despite reduced playing time, bench players performed similar amounts of maximal and supramaximal exercise when compared to starters (p≥0.279). Player position, role and match periods influence the demands of women's basketball; these factors should be considered when designing match-specific conditioning programs.

Construct Validity of Accelerometry-Derived Force to Quantify Basketball Movement Patterns

This study assessed the construct validity of accelerometry-derived net force to quantify the external demands of basketball movements. Twenty-eight basketballers completed the Yo-Yo intermittent recovery test (Yo-Yo-IR1) and basketball exercise simulation test (BEST). Intensity was quantified using accelerometry-derived average net force (AvF_Net) and PlayerLoad^TM per minute (PL/min). Within-player correlations were determined between intensity and running speed during Yo-Yo-IR1. Measured AvF_Net was determined for movements during the BEST and predicted AvF_Net was calculated using movement speed and correlations from Yo-Yo-IR1. Relationships between AvF_Net and running speed during Yo-Yo-IR1 were nearly perfect (r²=0.95, 95% CI: 0.94-0.96; p<0.001) and stronger than correlations between running speed and PL/min (r²=0.80, 95% CI: 0.73-0.87; p<0.001). Differences between measured and predicted AvF_Net were small during jogging and running (<1%), but large for basketball movements including jumping, change-of-direction and shuffling (15%-41%). As hypothesised, AvF_Net differed by playing position (11%-16%; p<0.001) and reflected the additional demand upon players with larger body mass and lower movement efficiency. Both sprint speed and AvF_Net reduced during the course of the BEST (p≤0.013). These findings confirm the construct validity of AvF_Net to quantify the external demand of basketball movements. Accelerometry-derived net force has the potential to quantify the external demands of basketballers during training and competition.

Strongyloides stercoralis: identification of a protease that facilitates penetration of skin by the infective larvae

Host invasion and tissue migration of several helminths have been linked to the expression and release of parasite-derived proteases. One of the most remarkable examples of tissue migration is that of larvae of the nematode parasite Strongyloides stercoralis, which can move through tissue at speeds of up to 10 cm per hour. We have shown the Strongyloides L3 larvae secrete a potent histolytic metalloprotease to facilitate their rapid migration. This protease has elastase activity and catalyzes the degradation of a model of dermal extracellular matrix. The importance of this enzyme in the pathogenesis of strongyloidiasis is underscored by the observation that invasion by larvae of skin in vitro is prevented by metalloprotease inhibitors. These results substantiate the role of proteases as virulence factors in strongyloidiasis, as well as other related parasitic infections, and suggest new approaches to therapy.