Passage Summary: Since people sitting in offices get more back injuries than people doing heavy manual labor, the author blames the office chairs and desks.

Conclusion: The design of office furniture and equipment is inadequate for protecting worker health.

Reasoning: Office workers who sit for long periods experience a higher rate of lower-back injuries than workers whose jobs involve heavy physical stress on the back.

Analysis: The author observes a higher injury rate in offices and immediately blames the furniture, but this ignores a sea of other variables. Perhaps the issue isn't the chair, but the act of sitting itself, or maybe manual laborers develop stronger muscles that protect their spines. To weaken this, look for an alternative explanation for the injury gap that has nothing to do with furniture design. If manual labor actually strengthens the back, the author's comparison between the two groups becomes much less convincing.