Charlie and others,
Could EMS in the pulsing mode for 10-20 mins. on each muscle group be used as a substitute for Tempo training? There is 6 inches of snow outside and no grass to run Tempo on. I’ve heard of Circuit Training as another alternative but would not know how to administer this.
There are still some better options for tempo work that you could implement, before opting for only EMS (although you could still use the EMS with the alternative solutions). One alternative that Charlie had identified was simply doing running on the spot (i.e. running A’s on the spot - with slightly lower knee lift). They could be done similar to treadmill work, with pushups or situps done in between reps (i.e. 30-60 seconds of running on the spot, with 20 pushups or 40 crunches in between sets).
The only precaution you have to take is to perform the running on the spot on a soft surface (i.e. soft matting underneath the feet) to cushion the impact and prevent shinsplints. Because the volume of foot contacts will definitely make your calves/achilles sore if you are not careful.
You can always do some light EMS pulsing after this work to help with flushing out the muscles.