Changes in EMG and Finger Force with Repeated Hangs from the Hands in Rock Climbers

The nature and degree of fatigue in muscles that control finger position during repeated sustained efforts in rock climbing have not been described. The purpose of this study was to identify changes in maximum hang time and forearm electromyogram (EMG) during repeated maximum duration hangs from a simulated rock feature. A second objective was to determine the effect of different recovery times between hangs upon changes in finger force. Five experienced rock climbers performed 2 test sessions on different days in a randomized order. Each session involved 8 repetitions of a maximum duration hang with either 1 min (R1) or 3 min (R3) resting recovery between hangs. Finger force (FF) was measured for the right hand via a piezoelectric force sensor fitted with a plate to accept the distal digits of four fingers. Peak EMG (EMGPK) and EMG Area (EMGAREA) were recorded from the anterior forearm for each hang and standardized as percent of maximum FF EMG prior to statistical analysis. Hang duration progressively decreased over repetitions but tended to plateau around repetition 5 for both R1 and R3 conditions. A significant difference was found for both recovery conditions and repetitions (p\u3c.05) as well as a significant interaction of the two factors (p\u3c.05) for hang duration. There were no significant differences for EMGPK among repetitions or between recovery conditions (p\u3e.05). EMGAREA decreased initially with repeated hangs during both R1 and R3 but this trend tended to plateau at repetition 3 for the R3 condition. A significant difference was found in EMGAREA for both recovery conditions and trials (p\u3c.05) as well as a significant interaction of the two factors (p\u3c.05). Mean FF decreased between pre- and post-hangs for both R1 and R3 however the difference was not significant. It was concluded that the overall decline in hang time is less with 3 min recovery vs 1 min recovery between hangs. Peak EMG does not appear to change despite this evidence of fatigue. A 3 min recovery interval between hang repetitions decreases the magnitude of fatigue experienced and enables a greater EMGAREA per hang

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data