Some thoughts on potential group goals:

-- Increasing the average workout time per day for the whole group by x percent in y weeks

-- All x team-mates run/swim/cycle/etc. for y minutes (non-stop) together

-- For x days in a row, at least y members of the group show up for the activity

-- Losing x pounds in total in y weeks

-- Assess each other (anonymously) with points on week 1, assess again in week 4 --> Group goal can be to improve total    group point by x percent