I personally think it is essential to keep a training log when you are training so that you can track your progress. When you use a log you can write everything down and see where you are looking good and what needs more improvement. Sometimes when you are training if you don't keep a log of everything you won't track the progress properly. By the time you get to the end of the week you will have forgotten what you lifted or ran at the start of the week.
Logs are great for tracking your rep ranges, sets, rest times and exercises being performed. Go out and get yourself a paper log and use it in and out of your training schedule. Keep it on you at all times so you can write new exercises down and keep a note of what you are doing.
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