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Sensorimotor adaptations to microgravity in humans

V. R. Edgerton^1,2,3,*, G. E. McCall², J. A. Hodgson¹, J. Gotto², C. Goulet², K. Fleischmann² and R. R. Roy¹

¹ Brain Research Institute,
² Department of Physiological Science and
³ Department of Neurobiology, University of California, Los Angeles, CA 90095-1527, USA

View larger version (18K): [in a new window]   Fig. 1. Mean torque during plantarflexion motor control tests performed at 10 and 50% maximal voluntary contraction (MVC) on test days pre-flight (L-30 and L-12), in-flight (F7/8 and F13/14) and post-flight (R+0, R+2, R+8, and R+15). The filled bar on the x-axis indicates flight days. Values are means ± S.E.M.; N=4 at each time point. Blue symbols indicate a significant difference between pre- and in-flight values. Green symbols indicate a significant difference between pre- and post-flight values. Orange symbols indicate a significant difference between in- and post-flight values. For 10% MVC, post-flight was elevated over pre-flight (P=0.03) and in-flight (P=0.009) values. For 50% MVC, pre-flight values were lower than in-flight (P=0.02) and post-flight (P=0.002) values. The P levels for the ANOVA main effects are shown.

View larger version (21K): [in a new window]   Fig. 2. Mean electromyographic (EMG) activity of the soleus (Sol), medial gastrocnemius (MG) and tibialis anterior (TA) muscles relative to maximal voluntary contraction (%MVC) during plantarflexion motor control tests performed at 10 and 50% MVC. The x-axis is labeled as for Fig.1. Values are means ± S.E.M.; N=4, except for F2/3 (N=3). R+15 was excluded for the TA as only one subject’s recordings were valid. Colored symbols indicate significant differences as in Fig.1. Red lines identify significant contrasts between pairs of adjacent data points. For the Sol, in-flight EMG amplitude was elevated above pre-flight values for both the 10% (P=0.02) and 50% MVC (P=0.002) tasks. No differences were observed in MG EMG amplitude. For the TA, in-flight (P=0.01) and post-flight (P=0.05) EMG amplitudes were elevated above pre-flight values for the 50% MVC task. The P levels for the ANOVA main effects are shown.

View larger version (18K): [in a new window]   Fig. 3. Mean torque during dorsiflexion motor control tests performed at 10 and 50% maximal voluntary contraction (MVC). The x-axis is labeled as for Fig.1. Values are means ± S.E.M.; N=4, except for F2/3 (N=3). No significant differences were observed. The P levels for the ANOVA main effects are shown.

View larger version (18K): [in a new window]   Fig. 4. Mean electromyographic (EMG) activity of the soleus (Sol), medial gastrocnemius (MG) and tibialis anterior (TA) muscles relative to maximal voluntary contraction (%MVC) during dorsiflexion motor control tests performed at 10 and 50% MVC. The x-axis is labeled as for Fig.1. Values are means ± S.E.M.; N=4, except for F2/3 (N=3). R+15 was excluded for the TA as only one subject’s recordings were valid. Colored symbols and lines indicate significant differences as in Fig.2. The Sol mean EMG amplitude was lower pre- than in-flight for the 10% (P=0.0001) and 50% (P=0.0002) MVC tasks. The MG mean EMG amplitude was lower pre- than in-flight for the 10% (P=0.05) and 50% (P=0.002) MVC tasks. The TA mean EMG amplitude was lower pre- than in-flight for the 10% (P=0.03) and 50% (P=0.02) and lower pre- than post-flight for the 50% (P=0.05) MVC tasks. The P levels for the ANOVA main effects are shown.

View larger version (14K): [in a new window]   Fig. 5. Mean integrated electromyographic (EMG) activity (mVs) observed over the entire recording day for the soleus (Sol), medial gastrocnemius (MG) and tibialis anterior (TA) muscles. The x-axis is labeled as for Fig.1. Only subjects with full data sets were used in determining mean values. Values are means ± S.E.M.; N=4, except for F7/8 (N=3). Colored symbols and lines indicate significant differences as in Fig.2. The in-flight values for the Sol (P=0.07) and TA (P=0.002) for each day were greater than the pre- and post-flight values. No differences were observed for the MG EMG activation levels. The P levels for the ANOVA main effects are shown.

View larger version (15K): [in a new window]   Fig. 6. The duration of electromyographic (EMG) activity (min) observed over the entire recording day for the same muscles as in Fig.5. The x-axis is labeled as for Fig.1. Values are means ± S.E.M.; N=4, except for F7/8 (N=3). Colored symbols and lines indicate significant differences as in Fig.2. The duration of activity for the Sol in-flight was greater than pre-flight (P=0.03). No differences in the duration of the active EMG periods were observed for the MG. The in-flight TA EMG duration was greater than pre- or post-flight values on each test day (P=0.0001). The P levels for the ANOVA main effects are shown.