While looking for ways to modify, buy, or build suitable seating for older people–I ran across this: http://www.wfu.edu/~marshap/MattErin.htm
And the conclusions (but not yet specific enough)–
Based on displacement and velocity data of the study participant, one could speculate that rising from the rocking chair was a more difficult task than rising from the standard chair. The lower and more posteriorly slanted seat of the rocking chair and the more forward movement of the knees during the rocking chair condition contributed to greater hip, knee, and ankle flexion (Wheeler et al., 1984; Rodosky et al., 1991). Larger torques at lower extremity joints likely occurred as a result, and more knee extensor muscle activation would be necessary during the extension phase (Wheeler et al., 1984). Using arm supports on rocking chairs would help to decrease joint torques (Bahrami et al., 2000). While greater momentum is generated in the rocking chair, quicker completion of the sit-to-stand transfer does not imply less stress on the joints. While rocking chairs may be comfortable for sitting, they do not provide the best conditions for standing up. For those who lead sedentary lifestyles, the elderly, or those with limited lower extremity range of motion, chair types other than rocking chairs would help to facilitate the sit-to-stand movement.