Activities before joining a challenge should not count towards that challenge

Some can do few activities after joining a challenge, but sync some time later or do long activity, so it still can change position a lot.

And if it would count only after joining, then joining during challenge would be pointless, so this would rather be closing entry to a challenge after one day or two from start.

Don't need to close entry to challenges. Just that makes no sense to join last minute and count whole month of activies. I think the challenge point is to incentivate people to do some activities. You can still join in the end, just not bring the pointless month of activities, that served no purpose, besides yourself. 

If you join in the end it's your decision. But for the people that have been actively participating in the challenge, that entry is pointless, nobody saw your evolution during the challenge. It served no purpose for that challenge. 

Like a race. You can still start later if that makes sense to you. But the idea is having everybody competing together. Not some folks appearing in the last stride, even if they did the double of the distance coming from different courses.

I think this should be changed because I'm quitting this challenge thing. For me it makes no sense this way. 

Maybe there could be points check with a leader of a challenge to enter.

So a user would need to have last synced at day when joining, and to have points not more then about a leader has. If a user would be much more active then everybody else on a challenge, then he couldn't enter half way.

This way it would still make sense to enter during a challenge and have chances to go top, and there won't be situation when someone enter and instantly outmatch other users.

I don't know how often this happens though, as I only done weekly steps challenges.