Influence of wheel rim width on rolling resistance and off-road speed in cross-country mountain biking.

The rim width of cross-country mountain bike wheel sets has increased in recent years, but the effect of this increase on performance remains unknown. The aim of this study was to analyse the influence of rim width on rolling resistance and off-road speed. We compared 3 tubeless wheel sets: 25 mm inner width as baseline, 30 mm width with the same tyre stiffness, and 30 mm width with the same tyre pressure. Three riders conducted 75 rolling resistance tests for each wheel set on a cross-country course. We determined rolling resistance using the virtual elevation method and calculated off-road speeds for flat and uphill conditions using a mathematical model. Baseline rolling resistance (Cr) was 0.0298, 90% CI [0.0286, 0.0310], which decreased by 1.4%, [0.7, 2.2] with the wider rim and the same tyre stiffness and increased by 0.9%, [0.1, 1.6] with the wider rim and the same tyre pressure. The corresponding effects on off-road speed were most likely trivial (0.0% to 0.7% faster and 0.1% to 0.6% slower, respectively). Because the effect of rim width on off-road speed seems negligible, athletes should choose the rim width that offers the best bike handling and should experiment with low tyre pressures.

Acute effects of walking at moderate normobaric hypoxia on gait and balance performance in healthy community-dwelling seniors: A randomized controlled crossover study.

BACKGROUND: Hiking at moderate altitude is a popular outdoor activity in seniors. Acute exercise or altitude can diminish balance performance. Thus, the present study examined the combined effects of altitude and walking on static and dynamic balance. METHODS: Thirty-six healthy seniors (age: 62 (SD: 4) y; BMI: 25 (5) kg/m(2)) were examined on three days. Firstly, walking velocity was determined at 85% of the first ventilatory threshold (VT1). Therefore, a ramp walking test on a treadmill was completed. On day two or three, a 40-minute treadmill walk under sea level or normobaric hypoxia (2600m) was performed using a random, double-blind study design. Balance performance was assessed on a force-plate during single leg stance with eyes open (SLEO, 10s on a force-plate) immediately before and after walking. Spatio-temporal gait characteristics were collected during walking at 5 and 35min. RESULTS: Condition×time interaction effects were not found for either parameter (0.13