When the dog increases speed, he may briefly pass through a period of "shuffling". This is just a running walk, and is perfectly normal, although most animals built for speed don't do it very much or for very long. It's no different than the running walk of the Icelandic horse, in which it has been genetically selected and intensified. In wild animals, it is typical of really big animals, such as elephant and grizzly, whose mass makes suspension difficult or impossible.
More typically, when increasing speed the dog may shift into a pace, with the legs on the same side moving in synchronization (Fig 3). This is not abnormal, nor is it an indication of structural problems. All dogs pace at one time or another. It's a gait that offers more speed than the walk without the energy consumption of the trot, which is probably why it is seen as a lazy gait. It appears clumsy because the body shifts from side to side, in exactly the same fashion as the camel, nature's best pacer. In fact, what is happening is quite interesting. Normally, a leg, front or rear, must be hauled forward by muscular work, and then thrust forward with more muscular work. But at the pace, the slight shift of the body to one side allows the legs of the opposite side to be swung forward by pendulum action, with very little muscular exertion. The camel uses this gait because of the incredibly harsh nature of its environment and the shortage of resources. It cannot afford to expend a drop more energy than is required. Generally, it is movement without any period of suspension. This would require extra speed and exertion, which the pace is not intended to provide. The Standardbred pacing horse specializes in a highly artificial, high speed, suspended pace because of breeding, training and special harnesses. For the horse, this gait prevents hoof interference and injury, allowing a huge overreach which is more difficult to achieve at the trot. These concerns don't apply to dogs, who use the pace as a more leisurely means of covering ground. For this reason it is not uncommonly seen in tired, aged, sick or unsound animals, and has been construed as an undesirable gait which is necessarily the result of these problems. This is simply not the case.

These concerns don't apply to dogs, who use the pace as a more leisurely means of covering ground. For this reason it is not uncommonly seen in tired, aged, sick or unsound animals, and has been construed as an undesirable gait which is necessarily the result of these problems. This is simply not the case.

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These concerns don't apply to dogs, who use the pace as a more leisurely means of covering ground. For this reason it is not uncommonly seen in tired, aged, sick or unsound animals, and has been construed as an undesirable gait which is necessarily the result of these problems. This is simply not the case.

Well that answers the questions about structural issues, thanks for the link and clip