service = ExerciseRecommenderService.new
exercises = Workout.last.exercises
service.recommend_next_exercise(exercises)
=> 
  [
    "Dumbbell shoulder press",
    "Sit on a bench with a dumbbell in each hand, palms facing forward. Start with the dumbbells at shoulder level. Push the dumbbells overhead until your arms are fully extended. Return to the starting position and repeat."
]