Historical clue formulations

• Distinct melodic segment — 2021-03-28
• Go all out — 2021-03-07
• Variation — 2019-05-11
• Group of viruses — 2009-11-08
• Lineage — 2008-02-03
• Virus variety — 2007-05-06
• Cause of muscle ache — 2003-11-25
• Muscle problem — 2001-11-28
• Back problem — 1999-06-12
• Push beyond limits — 1997-06-11
• Exertion — 1996-04-08