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Table 1.

Fitting terms from least squares linear regressions of log₁₀Maximum force output (N) as a function of log₁₀ Motor mass (kg) for different types of motors

Motor type	Intercept	Slope	r²	N	s.e.m. slope	Min mass	Max mass
Group 1
Muscles	2.995	0.677	0.997	16	0.010	4.8×10⁻²²	0.014
Rockets	2.737	0.719	0.988	19	0.019	0.0079	5.87×10⁵
Winches	3.251	0.736	0.852	6	0.154	14.5	1361
Linear actuators	3.048	0.612	0.656	9	0.167	0.34	2587
Mean	3.008	0.686
Group 2
Running animals	1.703	0.949	0.998	5	0.023	0.00004	32.7
Swimming animals	1.672	0.924	0.992	8	0.033	0.0009	0.04
Flying birds	1.555	0.959	0.993	11	0.026	0.002	0.37
Flying bats	1.862	1.082	0.994	7	0.037	0.002	0.013
Flying insects	1.583	0.959	0.982	149	0.011	3.7×10⁻⁷	0.008
Turbines	1.811	0.963	0.993	21	0.018	0.002	4264
Turbofans	1.793	0.986	0.934	30	0.049	64	6804
Electric rotary motors	1.739	1.078	0.999	10	0.013	0.04	558
Linear induction motors	1.825	0.854	0.940	7	0.096	1.9	32.6
Piston engines	1.719	1.016	0.988	31	0.021	0.165	2744
Mean	1.726	0.977

Motor type	Intercept	Slope	r²	N	s.e.m. slope	Min mass	Max mass
Group 1
Muscles	2.995	0.677	0.997	16	0.010	4.8×10⁻²²	0.014
Rockets	2.737	0.719	0.988	19	0.019	0.0079	5.87×10⁵
Winches	3.251	0.736	0.852	6	0.154	14.5	1361
Linear actuators	3.048	0.612	0.656	9	0.167	0.34	2587
Mean	3.008	0.686
Group 2
Running animals	1.703	0.949	0.998	5	0.023	0.00004	32.7
Swimming animals	1.672	0.924	0.992	8	0.033	0.0009	0.04
Flying birds	1.555	0.959	0.993	11	0.026	0.002	0.37
Flying bats	1.862	1.082	0.994	7	0.037	0.002	0.013
Flying insects	1.583	0.959	0.982	149	0.011	3.7×10⁻⁷	0.008
Turbines	1.811	0.963	0.993	21	0.018	0.002	4264
Turbofans	1.793	0.986	0.934	30	0.049	64	6804
Electric rotary motors	1.739	1.078	0.999	10	0.013	0.04	558
Linear induction motors	1.825	0.854	0.940	7	0.096	1.9	32.6
Piston engines	1.719	1.016	0.988	31	0.021	0.165	2744
Mean	1.726	0.977

N shows the sample size within each category of motor; s.e.m. is the standard error of the least squares regression slope. Minimum and maximum motor masses (kg) are shown for each category. Single molecules that create translational motion (myosin, kinesin, dynein, RNA polymerase) are included here with muscle cells and whole muscles (treating muscles alone yields a nearly identical scaling equation). Piston engines greater than 4400 kg mass are excluded because they scale differently than smaller piston engines (see text and Fig. 10).

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