An indoor rower, or rowing machine, is a machine used to simulate the action of watercraft rowing for the purpose of exercise or training for rowing. Indoor rowing has become established as a sport in its own right. The term also refers to a participant in this sport.
Modern indoor rowers are often known as ergometers (colloquially erg or ergo), an ergometer being a device which measures the amount of work performed. The indoor rower is calibrated to measure the amount of energy the rower is using through their use of the equipment.
Chabrias, an Athenian admiral of the 4th century BC, introduced the first rowing machines as supplemental military training devices. "To train inexperienced oarsmen, Chabrias built wooden rowing frames on shore where beginners could learn technique and timing before they went on board ship." 
Early rowing machines are known to have existed from the mid-1800s, a US patent being issued to W.B. Curtis in 1872 for a particular hydraulic based damper design. Machines using linear pneumatic resistance were common around 1900—one of the most popular was the Narragansett hydraulic rower, manufactured in Rhode Island from around 1900–1960. However they did not simulate actual rowing very accurately nor measure power output.
In the 1950s and 1960s, coaches in many countries began using specially made rowing machines for training and improved power measurement. One original design incorporated a large, heavy, solid iron flywheel with a mechanical friction brake, developed by John Harrison of Leichhardt Rowing Club in Sydney, later to become a professor of mechanical engineering at the University of New South Wales. Harrison, a dual Australian champion beach sprinter who went on to row in the coxless four at the 1956 Melbourne Olympics, had been introduced to rowing after a chance meeting with one of the fathers of modern athletic physiological training and testing, and the coach of the Leichhardt Guinea Pigs, Professor Frank Cotton. Professor Cotton had produced a rudimentary friction-based machine for evaluating potential rowers by exhausting them, without any pretence of accurately measuring power output. Harrison realised the importance of using a small braking area with a non-absorbent braking material, combined with a large flywheel. The advantage of this design (produced by Ted Curtain Engineering, Curtain being a fellow Guinea Pig) was the virtual elimination of factors able to interfere with accurate results—for instance ambient humidity or temperature. The Harrison-Cotton machine represents the very first piece of equipment able to accurately quantify human power output; power calculation within an accuracy range as achieved by his machine of less than 1% remains an impressive result today. The friction brake was adjusted according to a rower's weight to give an accurate appraisal of boat-moving ability (drag on a boat is proportional to weight). Inferior copies of Harrison's machine were produced in several countries utilising a smaller flywheel and leather straps—unfortunately the leather straps were sensitive to humidity, and the relatively large braking area made results far less accurate than Harrison's machine. The weight correction factor tended to make them unpopular among rowers of the time. Harrison, arguably the father of modern athletic power evaluation, died in February 2012.
In the 1970s, the Gjessing-Nilson ergometer from Norway used a friction brake mechanism with industrial strapping applied over the broad rim of the flywheel. Weights hanging from the strap ensured that an adjustable and predictable friction could be calculated. The cord from the handle mechanism ran over a helical pulley with varying radius, thereby adjusting the gearing and speed of the handle in a similar way to the changing mechanical gearing of the oar through the stroke, derived from changes in oar angle and other factors. This machine was for many years the internationally accepted standard for measurement.
In 1981, Peter and Richard Dreissigacker, and Jonathan Williams, filed for U.S. patent protection, as joint inventors of a "Stationary Rowing Unit". The patent was granted in 1983 (US4396188A). The first commercial embodiment of the Concept2 "rowing ergometer" (as it came to be known) was the Model A, a fixed-frame sliding-seat design using a bicycle wheel with fins attached for air resistance. The Model B, introduced in 1986, introduced a solid cast flywheel (now enclosed by a cage) and the first digital performance monitor, which proved revolutionary. This machine's capability of accurate calibration combined with easy transportability spawned the sport of competitive indoor rowing, and revolutionised training and selection procedures for watercraft rowing. Later models were the C (1993) and D (2003). 
In 1995, Casper Rekers, a Dutch engineer, was granted a U.S. patent for a "Dynamically Balanced Rowing Simulator" (US5382210A). This device differed from the prior art in that the flywheel and footrests are fixed to a carriage, the carriage being free to slide fore and aft on a rail or rails integral to the frame. The seat is also free to slide fore and aft on a rail or rails integral to the frame. From the patent Abstract: "During exercise, the independent seat and energy dissipating unit move apart and then together in a co-ordinated manner as a function of the stroke cycle of the oarsman.". "RowPerfect" and "Oartec" are two companies which currently manufacture commercial embodiments of the Rekers device.
All rowing-machine designs consist of an energy damper or braking mechanism connected to a chain, strap, belt and/or handle. Footrests are attached to the same mounting as the energy damper. Most include a rail which either the seat or the mechanism slide upon. Different machines have a variety of layouts and damping mechanisms, each of which have certain advantages and disadvantages.
Currently available ergometer (flywheel-type) rowing machines use a spring or elastic cord to take up the pull chain/strap and return the handle. Advances in elastic cord and spring technology have contributed to the longevity and reliability of this strategy, but it still has disadvantages. With time and usage, an elastic element loses its strength and elasticity. Occasionally it will require adjustment, and eventually it will no longer take up the chain with sufficient vigour, and will need to be replaced. The resilience of an elastic cord is also directly proportional to temperature. In an unheated space in a cold climate, an elastic cord equipped rowing ergometer is unusable because the chain take-up is too sluggish. Thus, as the result of several factors, the force required to stretch the elastic cord is a variable, not a constant. This is of little consequence if the exercise device is used for general fitness, but it is an unacknowledged problem, the "dirty little secret", of indoor rowing competitions. The electronic monitor only measures the user input to the flywheel. It does not measure the energy expenditure to stretch the elastic cord. A claim of a "level playing field" cannot be made when a resistance variable exists (that of the elastic cord) which is not measured or monitored in any way (see more on this in "Competitions" section).
In the patent record, means are disclosed whereby the chain/cable take-up and handle return are accomplished without the use of a spring or elastic cord, thereby avoiding the stated disadvantages and defects of this broadly used method. One example is the Gjessing-Nilson device described above. Partially discernable in the thumbnail photo, it utilizes a cable wrapped around a helical pulley on the flywheel shaft, the ends of this cable being connected to opposite ends of a long pole to which a handle is fixed. The obvious disadvantage of this system is the forward space requirement to accommodate the extension of the handle pole at the "catch" portion of the stroke. The advantage is that, except for small transmission losses, all of the user's energy output is imparted to the flywheel, where it can be accurately measured, not split between the flywheel and an elastic cord of variable, unmeasured resistance. If a similar system were installed on all rowing ergometers used in indoor rowing competitions, consistency between machines would be guaranteed because the variability factor of elastic cord resistance would be eliminated, and this would therefore ensure that the monitor displayed actual user energy input.
In a 1988 US patent (US4772013A), Elliot Tarlow discloses another non-elastic chain/cable take-up and handle return strategy. Described and depicted is a continuous chain/cable loop that passes around the flywheel sprocket and around and between fixed pulleys and sprockets positioned fore and aft on the device. The handle is secured in the middle of the exposed upper horizontal section of the chain/cable loop. Although somewhat lacking in aesthetics, the Tarlow device does eliminate the stated disadvantages and defects of the ubiquitous elastic cord handle return. Tarlow further argues that the disclosed method provides an improved replication of rowing because in actual rowing the rower is not assisted by the contraction of a spring or elastic cord during the "recovery" portion of the stroke. The rower must push the oar handle forward against wind and oarlock resistance in preparation for the next stroke. Tarlow asserts that the invention replicates that resistance.
A third non-elastic handle return strategy is disclosed in US patent, "Gravity Return Rowing Exercise Device" (US9878200 B2, 2018) granted to Robert Edmondson. As stated in the patent document, the utilization of gravity (ie: a weight) to take up the chain and return the handle eliminates the inevitable variability of handle return force associated with an elastic cord system and thereby ensures consistency between machines.
Machines with a digital display calculate the user's power by measuring the speed of the flywheel during the stroke and then recording the rate at which it decelerates during the recovery. Using this and the known moment of inertia of the flywheel, the computer is able to calculate speed, power, distance and energy usage. Some ergometers can be connected to a personal computer using software, and data on individual exercise sessions can be collected and analysed. In addition, some software packages allows users to connect multiple ergometers either directly or over the internet for virtual races and workouts.
At the current state of the art, indoor rowers which utilize flywheel resistance can be categorized into two motion types. In both types, the rowing movement of the user causes the footrests and the seat to move further and closer apart in co-ordination with the user's stroke. The difference between the two types is in the movement, or absence of movement, of the footrests relative to ground.
The first type is characterized by the Dreissigacker/Williams device (referenced above). With this type the flywheel and footrests are fixed to a stationary frame, and the seat is free to slide fore and aft on a rail or rails integral to the stationary frame. Therefore, during use, the seat moves relative to the footrests and also relative to ground, while the flywheel and footrests remain stationary relative to ground. This type is sometimes referred to as a "stationary" or "fixed head" rowing ergometer.
The second type is characterized by the Rekers device (referenced above). With this type, both the seat and the footrests are free to slide fore and aft on a rail or rails integral to a stationary frame. Therefore, during use, the seat and the footrests move relative to each other, and both also move relative to ground. This type is often referred to as a "dynamic" rowing ergometer, although "dynamically balanced" would be a more accurate description. The effect, for the user, is a more realistic "on the water" sensation than that provided by a "stationary" rowing ergometer because the "dynamically balanced" type more closely replicates actual rowing wherein the seat and the boat move relative to each other, and both move relative to the water.
Included within the "dynamically balanced" category are indoor rowers in which the footrests and flywheel are fixed to a moveable carriage, and also those in which the footrests alone are fixed to the moveable carriage, the carriage in both cases being free to slide fore and aft on a rail or rails integral to the stationary frame. The described device in which the flywheel is fixed to and moves with the carriage and footrests (the Rekers design) is sometimes referred to as a "floating head" rowing ergometer.
Indoor rowers which utilize a pivoting handle or handles to simulate a sweep or sculling stroke (thus referred to as "rowing simulators"), can be of the above described "stationary" or "dynamically balanced" type of rowing ergometer. The Coffey rowing machine, designed by Olympic silver medalist rower, Calvin Coffey, can be configured to enable a sweep or a sculling stroke, in either a "stationary" or "dynamically balanced" mode. The flywheel is positioned horizontally at the rear of the device, under the seat rails (US patents: US4743011A 1988; US7862484B1; Inventor: Calvin Coffey).
The Rekers rowing ergometer (referenced above) is described in the title of the patent document as "dynamically balanced", rather than simply "dynamic", as is common among users. "Dynamically balanced" is the accurate description, for the following reason: During the drive portion of the stroke, since the sliding carriage to which the footrests are attached, and the sliding seat, can both move independently fore and aft on a rail or rails, therefore the straightening of the user's legs causes the footrests to slide forward, and simultaneously causes the seat to slide rearward. However, since the combined mass of the seat and user is considerably greater than the combined mass of the footrests and sliding carriage (and flywheel, if it is part of the sliding footrests assembly), therefore the rearward movement of the seat and user, relative to ground, is much less than the forward movement of the footrests and carriage assembly, relative to ground. During the recovery portion of the stroke, this difference in mass has the same effect. The sliding footrests carriage, and the sliding seat carrying the user move proportionately the same distances relative to ground as during the drive as they return to their starting positions. Thus, during use, the combined mass of the footrest and sliding carriage, and the combined mass of the user and sliding seat, move towards and away from each other, as they oscillate about their common centre of gravity. To ensure the linked movement of these two masses remain centred on the device, the rail or rails upon which they slide are sloped upward slightly at their front and rear ends. Alternatively, elastic cords or springs attached to the seat and footrests can ensure such centering.
In addition to the aforementioned improved "on the water" sensation experienced by the user of a "dynamically balanced" rowing ergometer, there are also bio-mechanical and power delivery advantages. Bio-mechanically, throughout all phases of the stroke, the user's mass moves only a small distance relative to ground, therefore the user is not subject to the inertial stresses associated with the abrupt fore and aft directional changes experienced on a "stationary" rowing ergometer. With respect to power delivery: Casper Rekers, inventor of the "dynamically balanced" rowing ergometer, "performed tests comparing the indicated power output of a "stationary" versus a "dynamic" rowing ergometer - the subject gained 10-20% power output in the second case, representing additional power that could be applied to the flywheel instead of accelerating the bodyweight" of the user on the seat rail.
Piston resistance comes from hydraulic cylinders that are attached to the handles of the rowing machine. The length of the rower handles on this class of rower is typically adjustable, however, during the row the handle length is fixed which in turn fixes the trajectory that the hands must take on the stroke and return, thus making the stroke less accurate than is possible on the other types of resistance models where it is possible to emulate the difference in hand height on the stroke and return. Furthermore, many models in this class have a fixed seat position that eliminates the leg drive which is the foundation of competitive on water rowing technique. Because of the compact size of the pistons and mechanical simplicity of design, these models are typically not as large or as expensive as the others types.
Braked flywheel resistance models comprise magnetic, air and water resistance rowers. These machines are mechanically similar since all three types use a handle connected to a flywheel by rope, chain, or strap to provide resistance to the user – the types differ only in braking mechanism. Because the handle is attached to the resistance source by rope or similarly flexible media, the trajectory of the hands in the vertical plane is free making it possible for the rower to emulate the hand height difference between the stroke and the return. Most of these models have the characteristic sliding seat typical of competitive on-the-water boats.
- Magnetic resistance models control resistance by means of electromagnets that engage a mechanical brake with the flywheel. The magnetic braking system is quieter than the other braked flywheel types. The braking resistance is adjustable and energy can be accurately measured on this type of rower. The drawback of this type of resistance mechanism is that the resistance is constant; rowers using air or water resistance more accurately simulate actual rowing, where the resistance increases the harder the handle is pulled.
- Air resistance models use vanes on the flywheel to provide the flywheel braking needed to generate resistance. As the flywheel is spun faster, the air resistance increases. An adjustable vent can be used to control the volume of air moved by the vanes of the rotating flywheel, therefore a larger vent opening results in a higher resistance, and a smaller vent opening results in a lower resistance. The energy dissipated can be accurately calculated given the known moment of inertia of the flywheel and a tachometer to measure the deceleration of the flywheel. Air resistance rowing machines are most often used by sport rowers (particularly during the off season and inclement weather) and competitive indoor rowers. RowPerfect, Oartec, and Concept 2, are three manufacturers of this type of rowing machine.
- Water resistance models consist of a paddle revolving in an enclosed tank of water. The mass and drag of the moving water creates the resistance. Proponents claim that this approach results in a more realistic action than possible with air or magnetic type machines. "WaterRower" was the first company to manufacturer this type of rowing machine. The company was formed in the 1980's by John Duke, a US National Team rower, and inventor of the device (1989 US Patent US4884800A). At that time, in the patent record, there were a few prior art fluid resistance rowing machines, but they lacked the simplicity and elegance of the Duke design. From the 1989 patent Abstract: "... rowing machine features a hollow container that holds a supply of water. Pulling on a drive cord during a pulling segment of a stroke rotates a paddle or like mechanism within the container to provide a momentum effect."
- Rheological fluid resistance: In the patent record various exercise devices, including rowing machines, are depicted and described utilizing flywheels in which rotational resistance is controlled by varying the viscosity of a magnetically or electrically reactive fluid (magnetorheological or electrorheological fluid). It seems probable therefore that at some time commercially available rowing machines will include those with flywheels containing variable viscosity fluid.
Rowing machines with monitors calculate performance using an algorithm unique to the individual manufacturer; it will be affected by the type of resistance used and other factors.
Indoor rowing primarily works the cardiovascular systems with typical workouts consisting of steady pieces of 20–40 minutes, although the standard trial distance for record attempts is 2000 m, which can take from five and a half minutes (best elite rowers) to nine minutes or more. Like other forms of cardio focused exercise, interval training is also commonly used in indoor rowing. While cardio-focused, rowing also stresses many muscle groups throughout the body anaerobically, thus rowing is often referred to as a strength-endurance sport.
Unlike high impact exercises, which can damage knees and the connective tissues of the lower body, rowing's most common injury site is the lower back. Proper technique is a necessity for staying injury free, with a focus on both mechanics and breathing, as correct rhythm, exhaling on the drive and inhaling on the recovery, is a stabilizing force for the upper body. Non-rowers commonly overemphasize the muscles of the upper body, while correct technique uses the large muscle of the thighs to drive much of the stroke. Also, good technique requires that the angle of the upper body is never too far forward, nor too far back, both of which jeopardize the lower back and compression injuries on the knees and hip flexor muscles. Proper technique however, can only be achieved if the design of the exercise equipment enables proper technique. The ubiquitous rigid, single-piece handle does not follow the natural movement of a user's hands, wrists, and forearms as the stroke progresses. It does not ensure or enable the bio-mechanically correct alignment of the hands, wrists, and forearms with the direction of the applied force. Typically, the user finishes the stroke with the wrists in an angulated position. It is incorrect to criticize this as "bad technique", when the equipment itself is the cause. Through no fault of their own, regular users of indoor rowers equipped with the standard single-piece handle, are prone to repetitive strain injury and chronic wrist pain (see more on this in "Rowing Technique" section, below).
In addition to the high levels of fitness attained, rowing is an intense calorie-burning exercise. The late Dr. Fritz Hagerman, Professor of biomedical science and a leading researcher in rowing physiology, determined that "...you burn more calories in rowing than any other activity. Cross-country skiing comes closest. At standard submaximal levels of exercise, rowing will burn calories at a rate 10-12% higher than running, and 15-20% higher than cycling."  Although rowers with less ability and training will burn fewer calories, the ergometer is an excellent tool for use in a weight-loss program.
The standard measurement of speed on an ergometer is generally known as the "split", or the amount of time in minutes and seconds required to travel 500 metres (1,600 ft) at the current pace — a split of 2:00 represents a speed of two minutes per 500 metres, or about 4.17 m/s (15.0 km/h). The split does not necessarily correspond to how many strokes the rower takes (the "rating") since strokes can vary in power.
Ergometer tests are used by rowing coaches to evaluate rowers and is part of athlete selection for many senior and junior national rowing teams. During a test, rowers will row a set distance and try to clock the fastest time possible, or a set time and try to row the longest distance possible. The most common distances for erg tests are 1000, 2000, 5000, 6000 or 10000 metres. The most common times for erg tests are 3 min, 5 min, 20 min, 30 min, and 1 hour.
Rowing technique on the erg broadly follows the same pattern as that of a normal rowing stroke on water, but with minor modifications: it is not necessary to "tap down" at the finish, since there are no blades to extract from water; but many who also row on water do this anyway. Also, the rigid, single-piece handle enables neither a sweep nor a sculling stroke. The oar handle during a sweep stroke follows a long arc, while the oar handles during a sculling stroke follow two arcs. The standard handle does neither. But regardless of this, to reduce the chance of injury, an exercise machine should enable a bio-mechanically correct movement of the user. The handle is the interface between the human and the machine, and should adapt to the natural movement of the user, not the user to the machine, as is now the case. During competitions an exaggerated finish is often used, whereby the hands are pulled further up the chest than would be possible on the water, resulting in a steep angulation of the wrists - but even with a normal stroke, stop-action images show wrist angulation at the finish, evidence that the standard rigid, single-piece handle does not allow the user to maintain a bio-mechanically correct alignment of hands, wrists, and forearms in the direction of applied force. On the Concept 2 website "Forum", many regular users of the indoor rower have complained of chronic wrist pain. Some have rigged handgrips with flexible straps to enable their hands, wrists, and forearms to maintain proper alignment, and thereby reduce the possibility of repetitive strain injury. Rowing machine manufacturers have ignored this problem.
Rowing on an ergometer requires four basics phases to complete one stroke; the catch, the drive, the finish and the recovery. The catch is the initial part of the stroke. The drive is where the power from the rower is generated while the finish is the final part of the stroke. Then, the recovery is the initial phase to begin taking a new stroke. The phases repeat until a time duration or a distance is completed.
Knees are bent with the shins in a vertical position. The back should be roughly parallel to the thigh without hyperflexion (leaning forward too far). The arms and shoulders should be extended forward and relaxed. The arms should be level.
The drive is initiated by the extension of the legs; the body remains in the catch posture at this point of the drive. As the legs continue to full extension, the rower engages the core to begin the motion of the body levering backward, adding to the work of the legs. When the legs are flat, the rower begins to pull the handle toward the chest with their arms while keeping their arms straight and parallel to the floor.
Finish (or release)
The legs are at full extension and flat. The shoulders are slightly behind the pelvis, and the arms are in full contraction with the elbows bent and hands against the chest below the nipples. The back of the rower is still maintained in an upright posture and wrists should be flat.
The recovery is a slow slide back to the initial part of the stroke, it gives the rower time to recover from the previous stroke. During the recovery the actions are in reverse order of the drive. The arms are fully extended so that they are straight. The torso is engaged to move forward back over the pelvis. Weight transfers from the back of the seat to the front of the seat at this time. When the hands come over the knees, the legs contract back towards the foot stretcher. Slowly the back becomes more parallel to the thighs until the recovery becomes the catch.
The first indoor rowing competition "was held in Cambridge, MA in February 1982 with participation of 96 on-water rowers" who called themselves the "Charles River Association of Sculling Has-Beens" . Thus the acronym, "CRASH-B". A large number of indoor rowing competitions are now held worldwide, including the indoor rowing world championships (still known as CRASH-B Sprints) held in Boston, Massachusetts, United States in February and the British Indoor Rowing Championships held in Birmingham, England in November, or in more recent years the Lee Valley VeloPark London in December; both are rowed on Concept2s. The core event for most competitions is the individual 2000-m; less common are the mile (e.g., Evesham), the 2500-m (e.g., Basingstoke—also the original distance of the CRASH-B Sprints). Many competitions also include a sprint event (100m-500m) and sometimes team relay events.
Most competitions are organized into categories based on sex, age, and weight class. While the fastest times are generally achieved by rowers between 20 and 40 years old, teenagers and rowers over 90 are common at competitions. There is a nexus between performance on-water and performance on the ergometer, with open events at the World Championships often being dominated by elite on-water rowers. Former men's Olympic single scull champions Pertti Karppinen and Rob Waddell and five-time Gold Medalist Sir Steven Redgrave have all won world championships or set world records in indoor rowing.
In addition to live venue competitions, many erg racers compete by internet, either offline by posting scores to challenges, or live online races facilitated by computer connection. Online Challenges sponsored by Concept2 include the annual ultra-rowing challenge, the Virtual Team Challenge.
Regarding comparability of results between machines: As stated, the above indoor rowing competitions use the Concept 2 rowing ergometer, currently the Model D, which like previous models, is equipped with an electronic performance monitor that compensates for differences in resistance adjustment (1989 US Patent US4875674A; Assignee: Concept 2). Therefore it is widely accepted that a result on one machine can be fairly compared with a result on another machine regardless of their respective resistance settings. The assumed consistency between machines would be correct if another, unmeasured resistance variable did not exist. This is the variability of the resistance of the elastic cord used to take up the chain and return the handle. The electronic performance monitor only measures the energy expended to spin the flywheel. It does this via small magnets embedded in the face of the flywheel which pass a sensor connected to the performance monitor (see patent US4875674A referenced above). The monitor does not measure the energy required to stretch the elastic cord, therefore unless the force required to stretch the elastic cord is a guaranteed constant, there is no guarantee that the performance monitor will display the actual total energy expended by the user.
Factors which affect the force required to stretch the elastic cord are: the tension of the cord, the amount of usage of the machine, ambient temperature. Typically, the elastic cord is factory adjusted to approximately seven pounds of return force. On the Concept 2 website "Forum" much anecdotal evidence has been posted of new machines feeling "heavier" than used machines, that more effort is required to achieve the same monitored result on a new machine than on one that has been worn-in. This is understandable. Any elastic element loses elastic strength with time and usage.
Variability between machines is of small importance if one machine is used consistently for fitness and training, such as in a home gym. It will still provide a sufficiently reliable measure of one's progress. In a competition setting however, equivalence between machines is essential. An example will clarify: Consider the entirely reasonable possibility that the elastic cord of one machine requires 7 pounds of force to stretch, and the elastic cord of another machine requires 6 1/2 pounds of force to stretch. Now suppose that two competitors, one on each of these machines, complete a 2000M race in 8 minutes at an average stroke rate of 30 strokes per minute. The competitor on the machine with the elastic cord tensioned to 7 pounds will need to pull with 1/2 pound more force for the duration of each stroke than the other competitor in order to obtain the same monitored results (since, as explained, only the energy expended to spin the flywheel is measured, not the energy to stretch the elastic cord). If each stroke averages 5 feet in length, and it takes 240 strokes (8X30) to complete the race, the extra work done by the one competitor is equivalent to lifting a 1/2 pound weight through a vertical distance of 1200 feet (5X240), or put another way, the extra work required by this competitor is equivalent to lifting a 10 pound weight through a vertical distance of 60 feet. However, in this example, despite the difference in energy output by the competitors, the monitor displays are the same.
While true that indoor rowing competitions use only new machines in an effort to ensure all elastic cord tensions are identical, this cannot be confirmed because tensions are never measured or adjusted at these competitions. Further, since ambient temperature affects cord elasticity, the results of races in different locations with different ambient temperatures are not comparable. Fairness is particularly problematic with on-line racing in which new machines and worn-in machines with elastic cords of differing strengths and tension can be used by competitors.
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