public async Task <IActionResult> Index()
        {
            if (!_cache.TryGetValue("exercise", out list))
            {
                list = await _exerciseService.FindAllAsync();

                _cache.Set("exercise", list, cacheOptions);
            }
            else
            {
                list = _cache.Get("exercise") as List <Exercise>;
            }
            return(View(list));
        }