Sometimes I like to put my clients on the treadmill for cardio and weight intervals. I like this for a few reasons:

1. Great for clients that you only see 1x/wk, you can get both weights and some cardio in.
2. Client can work at their pace if they are having a rough day (its time based)
3. You can adjust the incline and speed on the treadmill (insert evil smiling devil emoji face here)

I like to put the dumbbells in the cup holders for clients to access easier, but you can always hold them or set on the floor between intervals. I also have my athletes straddle the treadmill for their weight intervals and leave the treadmill running to use the clock. With a continuous running clock you have the client alternate between weight intervals and cardio intervals. Here is how it works:

Warm Up Walk 5mins

8 Rounds:

1 minute of dumbbell movements

3mins of walking

Cool Down Walk 5mins

Core Activity/Movements

Stretch

Here are the following dumbbell exercises I like to have my clients do with weights all dumbbells .

Bicep Curls (Alternating singles or dual)

Tricep extension (standing) or kickbacks (bent at waist)

Shoulder Press (Alternating singles or dual)

Bent Over Rows (bent at waist alternating singles or dual)

Anterior/Frontal Raises (alternating singles or dual)

Squats holding Dumbbells (step off treadmill for this, but leave treadmill running)

Lateral/Side Raises (alternating singles or dual)

Weighted Lunges (step off treadmill for this. Can be done static or alternating in place forward or backward)

Give it a try and let me know how it goes!