Note that the guardsman in the pic has fainted to "attention" or a reasonable facsimile thereof.
Several old Senior NCOs advised troops that if they dropped their rifle on parade, they were to immediately assume a similar "prone, unsupported" position beside it and NOT move until the "medics" came to help. Hot, bitumen-covered parade grounds are not ideal for this; grassy playing fields are better but lack the proper surface that provides the "snap and crump" of a thousand good boots 'shunning and un-'shunning in perfect synchronisation.
Standard training was to do little isometric exercised (muscle against muscle) to maintain blood-flow and alertness (and perpendicularity).