Table 6.

Results of regressions of peak tensile stress in the femur during locomotion on kinematic and force variables for P. concinna and I. iguana

P. concinnaI. iguana
VariableRMA slopeRPFRMA slopeRPF
FemTV angle (+) (deg.)–0.170.440.001*13.681.440.330.103.01
FemHZ angle (–) (deg.)–0.570.350.01*8.02–0.970.360.073.61
Knee angle (+) (deg.)–0.270.370.005*8.61–1.820.290.152.26
Ankle angle (+) (deg.)0.210.110.430.62–1.720.110.590.29
Fm kext (+) (BW)3.290.360.01*8.350.970.88<0.0001*82.40
Fm add (–) (BW)–4.810.57<0.0001*26.94–0.180.000.990.00
Fm aext (+) (BW)4.690.65<0.0001*41.831.490.620.001*15.26
Rhip (+) (CL)48.990.290.03*4.900.950.030.880.02
Rknee (–) (CL)–74.530.240.073.370.510.350.083.31
Rankle (+) (CL)186.060.290.03*5.08–0.510.120.550.36
Net GRF (+) (BW)20.420.480.0001*17.060.040.74<0.0001*29.44
GRF AP angle (+) (deg.)–0.490.050.710.141.070.200.321.04
GRF ML angle (–) (deg.)–0.410.100.470.54–0.650.140.480.51
Speed (+) (CL s–1)–45.010.010.940.010.050.340.093.19
  • All force and kinematic variables were determined at the time of peak tensile stress

    Muscle force and moment arm data normalized for body weight (BW) and carapace length (CL), respectively, for P. concinna only

    FemTV, hip protraction/retraction angle; FemHZ, hip abduction/adduction angle; Fm, force exerted by a muscle group; kext, knee extensors; add, femoral adductors; aext, ankle extensors; R, moment arm of GRF about a limb joint; net GRF, magnitude of resultant GRF vector; GRF AP, anterioposterior angle of GRF vector (in direction of travel); GRF ML, mediolateral angle of GRF vector (orthogonal to direction of travel)

    Positive variables (+): positive slopes indicate increasing values with increased stress; negative slopes indicate decreasing values with increased stress

    Negative variables (–): positive slopes indicate decreasing values with increased stress; negative slopes indicate increasing values with increased stress

  • * RMA slopes significant at P<0.05; N=58 for all P. concinna regressions; N=26 for all I. iguana regressions (data from Blob and Biewener, 2001)