Exposure of human spermatozoa to the cumulus oophorus results in increased relative force as measured by a 760 nm laser optical trap.

Spermatozoa change their movement characteristics in response to different environmental conditions. To investigate the relative force of spermatozoa exhibiting different motility patterns, a laser optical trap was used. A laser beam at 760 nm was directed through a microscope objective and focused above the spermatozoa to create a three-dimensional optical trap. Spermatozoa were trapped at 300 mW, and laser power was reduced until spermatozoa could escape. The force generated by the flagellar movement was proportional to the laser power at which the spermatozoa escaped from the trap. Three motility patterns were studied: linear, hyperactivated, and cumulus-related. Mean escape power for spermatozoa displaying linear motility was 59.5 +/- 43 mW, for hyperactivated motility 122.3 +/- 67 mW (P < 0.0001) and for cumulus-related motility 200.6 +/- 44.2 mW (P < 0.0001). In this study, we showed that human spermatozoa generated more relative force upon exposure to the cumulus mass. The combination of small-amplitude lateral head displacement and higher relative force may produce a 'drilling' effect which is synergistic with the enzymatic digestion of the cumulus matrix during the fertilization process.