Nat. Rev. Cardiol. doi:10.1038/nrcardio.2016.140 Figure 9 Assessing force production, velocity, and power output of the cardiac sarcomere Figure 9 | Assessing force production, velocity, and power output of the cardiac sarcomere. a | The equation on the left enables calculation of the ensemble force (Fe) of the sarcomere as the product of the intrinsic force of each myosin head (f), the total number of myosin heads functionally able to interact with actin filaments (N), and the ratio of the time spent in a strongly-bound state to the total cycle duration (ts/tc), which determines the proportion of myosin heads in a force-producing state. The lower equation estimates the unloaded velocity (v) from the myosin head stroke size (d) divided by the strongly-bound state time (ts). The power output of the sarcomere is represented by the area under the load–velocity curve. As the ensemble force and/or velocity increase, so does the power output, as shown in the graph. b | A dual-beam, three-bead optical trap. Both ends of a single actin filament are attached to 1 µm polystyrene beads, which are held in place by two focused infrared (IR) laser beams. Beneath this 'actin dumbbell' is a single myosin molecule attached to a 1.5 µm polystyrene platform bead fixed on a coverslip surface. The position-sensitive detectors can accurately gauge even 1 nm of movement in the beads. This assay allows direct measurement of the intrinsic force (f), strongly bound state time (ts), and stroke size (d) of a myosin head. GFP, green fluorescent protein. Panel a is adapted from Spudich, J. A. Hypertrophic and dilated cardiomyopathy: four decades of basic research on muscle lead to potential therapeutic approaches to these devastating genetic diseases. Biophys. J. 106, 1236–1249 (2014), with permission from Elsevier. Panel b is adapted from Sung, J. et al. Single-molecule dual-beam optical trap analysis of protein structure and function. Meth. Enzymol. 475, 321–375 (2010), with permission from Elsevier. Panel a is adapted from Spudich, J. A. Hypertrophic and dilated cardiomyopathy: four decades of basic research on muscle lead to potential therapeutic approaches to these devastating genetic diseases. Biophys. J. 106, 1236–1249 (2014), with permission from Elsevier. Panel b is adapted from Sung, J. et al. Single-molecule dual-beam optical trap analysis of protein structure and function. Meth. Enzymol. 475, 321–375 (2010), with permission from Elsevier Sen-Chowdhry, S. et al. (2016) Update on hypertrophic cardiomyopathy and a guide to the guidelines Nat. Rev. Cardiol. doi:10.1038/nrcardio.2016.140