There is an interesting thread on the message board relating to modifying the rowing stroke on the Indoor Rower to improve race pace. The Concept 2 indoor rowing machine was designed to provide specific training for oarsmen when weather conditions prevented them training on the water.Therefore the technique adopted was that of the rowing stroke as carried out in a boat. This technique is sound as can be seen by the number of on-water rowers at the top of the rankings and has resulted in little if any experimentation of different techniques suitable specifically for the rowing machine.Both the boat and the machine are powered by a series of impulses created by the rower who moves up and down the slide. This means that both the boat and the flywheel velocity can be represented by a sine wave ranging between maximum and minimum velocity. This movement has a different effect on a boat's performance than the flywheel of a rowing machine. Newton's third law of motion states, every action has an equal and opposite reaction. As the oarsman changes direction at the beginning of the stroke, an equal and opposite force is created on the footplate. This is a negative impulse and has the effect of slowing down the boat. At the finish, when the oarsman moves his weight forward, an equal and opposite force is created which is a positive impulse that accelerates the boat. The positive and negative impulses extenuate the maximum and minimum velocity of the boat. These two impulses do not cancel each other out and result in a net loss. This is further aggravated by the fact that the change in the centre of gravity of the crew moving in the boat causes the pitch of the boat to alter which loses energy. To minimise the effect of this negative impulse, the oarsman has to control the speed at which he can travel forward. The speed of the recovery will be related to the speed of the boat and the only way an oarsman can increase the stroke rate is to increase the boat speed.In contrast, the rower on the machine, whilst still creating a negative impulse on the footplate at the beginning of the drive and a positive impulse on the recovery, this has no effect on the speed of the flywheel and therefore stroke rate on the rowing machine is not dependent on the flywheel speed. The most efficient way to rotate the flywheel is to apply a constant force to achieve a constant velocity because the air drag on the flywheel increases to the cube of acceleration. This cannot be achieved by rowing, but rowing at a higher rate on the machine is tending towards a constant force. This reduces the difference between the maximum and minimum velocity of the flywheel so this is tending towards a constant velocity. Air drag increases to the square of velocity and this has to be overcome, but the greater drag caused by acceleration is reduced and so the load is lighter. However, there is still the cost of effort, which increases with stroke rate. The best way to measure this is to wear a heart rate monitor and row on the machine at different stroke rates but without holding the handle and moving the flywheel. If you then compare the increase in heart rate and relate this to your heart rate through the training bands, you can estimate the amount of watts it is costing to row at the higher rate. To row 2,000 metres in seven minutes will require an average of 302 watts in addition to the watts estimated for the cost of effort.The other factor is related to the muscles, which have an optimum contraction velocity. This means that the muscles will work more efficiently at a certain stroke rate and less efficiently above and below this point. Muscles are also more efficient towards the end of their contraction range rather than at compression. Therefore, some people completing 2,000m at a higher stroke rate will achieve a better score even if the higher stroke rate is achieved by shortening the stroke. If this were your aim you would still benefit from training over the full range of movement and use the modified stroke for competition. If not and you train over a reduced range then you will effectively further reduce the efficient range of the muscles.