This is Golden Cheetah's definition:
[h=1]TRIMP[/h] TRIMP is an abbreviation for TRaining IMPulse. This term is quite generic but in general this metric accounts for both training intensity and volume based on heart rate based measures. The specific implementation in GoldenCheetah is the model of Morton/Bannister (citation needed) using the coefficients given by Green et al. (citation needed):
TRIMP = time * (AvgHR-RHR)/(MaxHR-RHR)*0.64*EXP(Ksex*(AvgHr-RHR)/(MaxHR-RHR)).
Here time is the workout duration in minutes, AvgHR is the mean HR for the workout, and Ksex is set to 1.92 for male or 1.67 for female. The constants MaxHR and RHR are the athletes maximum and resting heart rates as specified in the
athlete tab of the
options/preferences dialog.
It's a HR based version of the Training Stress Score (TSS) used with power meters, or more accurately, TSS is a power based version of TRIMP, since TRIMP came first. As everyone is saying, once you have a measure of your training load, it can be used to determine your training stress balance (TSB), which then is used to manage your training load and predict how fresh you will be for a race.
Trainingpeaks may be easier for you to use than GC, but you need the "premium" service, which is $119/year. WKO+ is a desktop version that adds even more features, costs $129 (one time), but isn't available for the Mac.
GC got funky for me with the last firmware release for my Garmin 500 - that may have been cleaned up by now, but I primarily use trainingpeaks anyway, because it is web based and I can access it from anywhere. I still haven't figure out how to make full use of WKO+. I need a lesson from Ex.