Ian Bernstein did some research into an Ergonomic Comparison of Rowing Machine Designs and possible implications for safety.
This has been published on the BJSM site. You may have to register to read the article,
but it’s free to register.
Update 2016 that link is no longer free.
Try this Researchgate link
Or read this pdf of the research An_ergonomic_comparison_of_rowing_machine_designs_