RESISTIVE EXERCISE MACHINES

Gideon Ariel, Ph.D. Coto Research Center

INTRODUCTION In more recent studies pertaining to exercise, The relationship between resistance exercises Pipes and Wilmore (75) compared isokinetic train- and muscle strength has been known for cen- ing to isotonic strength training in adult men. Ac- turies. In ancient Greece, Milo, the wrestler, used cording to their findings with isokinetic contrac- progressive resistance exercises to improve his tions at both low and high speeds, the isokinetic strength. His original method consisted of lifting training procedure demonstrated marked a calf each day until it reached its full growth, and superiority over the isotonic methods. In 1972, this technique provides probably the first example Ariel (3, 4, 5, 6, 7) introduced the Dynamic Variable of progressive resistance exercises. Today, it is Resistance exercise principles which resulted in- well documented in the literature that the size of the variable resistance exercise equipment skeletal muscle is effected by the amount of (Universal Gym Equipment's DVR Model). For the muscular activity performed. Increased work by a first time biomechanical principles were muscle can cause that muscle to undergo com- employed in the design of exercise equipment. pensatory growth (hypertrophy) while disuse leads to wasting of the muscle (atrophy). Definitions of Terms This information has stimulated the medical Due to ambiguity in the literature of certain and sports professions, especially coaches and physiological terms and laboratory procedural dif- athletes, to try many combinations and techni- ferences, the following terms have been defined: ques of muscle overload. These attempts to pro- Muscular Strength. The contracile power of duce a better means of rehabilitation or a muscles as a result of a single maximum ef- physiological edge in sporting activities have only fort. scratched the surface of the cellular mechanisms Muscular Endurance. Ability of the muscles and physiological consequences of muscular to perform work by holding a maximum con- overload. The 434 voluntary muscles in man con- traction for a given length of time or by con- stitute 40 to 60 percent of his total body weight. tinuing to move a submaximal load. These muscles are responsible for human motion, Isometric Training. A muscular contraction of which is the most fundamental function of the total effort but with no visible limb move- musculoskeletal system. ment (sometimes called static training). Muscular strength may be defined as the force Isotonic Training. Raising and lowering a sub- a muscle group can exert against a resistance in a max~malload, such as a weight. a given maximal effort. In 1948, Delorme (35) adopted the number of times (sometimes called dynamic name "progressive resistance exercise" for his training). method of developing muscular strength through lsokinetic Training (Accommodating the utilization of counter balances and weight of Resistance). Muscular contraction at a con- the extremity with a cable and pulley arrangement stant velocity. As the muscle length and, thus, gave load-assisting exercises to muscle changes, the resistance alters in a manner groups which did not perform antigravity motions. which is directly proportional to the force ex- McQueen (6) distinguished between exercise erted by the muscle. regimens for producing muscle hypertrophy and Concentric Contraction. An isotonic cont rac- those for producing muscle power. He concluded tion in which the muscle length decreases that the number of repetitions for each set of exer- (i.e., the muscle primarily responsible for cise determines the different characteristics of movement becomes shorter). the various training procedures. Eccentric Contraction. An isotonic contrac- Based on evidence presented in these early tion in which the muscle length increases studies, hundreds of investigations have been (i.e., the muscle primarily responsible for published relative to techniques for muscular movement becomes longer). development including isotonic exercises, Muscle Overload. The workload for a muscle isometric exercises, eccentric contractions, the o r muscle jroup whi ch is greater than that to Oxford technique, the double and triple pro- wlhich the rnuscle is accustomed. gressive super set system, and many others. Each Repetitions ,. The nlumber of consecutive system's effectiveness has Seen supported and times a pz ~rticularn novement or exercise is refuted by numerous investigations. Berger (13) perrormea.__t_--_> concluded that 6-7 repetitions three times a week Repetition Maximum (1RM). The maximum was best for developing dynamic strength. resistance a muscle or muscle group can Research conducted by Steinhause (86) emphasiz- overcome in a maximal effort. ed the need to increase the intensity-not the Sets. The number of groups of repetitions of amount of work-in order to develop maximum a particular movement or exercise. strength. Variable Resistance Exercise. As the muscle contracts, the resistance changes in a muscle and gravitational forces are important in predetermined manner (linear, exponentially, producing these turning effects which are fun- or in a user defined manner). damental in body movements in all sports and dai- 13. Variable Velocity Exercise. As the muscle con- ly living. Pushing, pulling, lifting, kicking, running, tracts with maximal or submaximal tension, walking. and all human activities are results of the speed of movement changes in a rotational motion of the links which are made of predetermined manner (linear, or exponen- bones. Since force has been considered the most tially, etc.). important component of athletic performance, 14. Vertical Jump. A jump executed in the vertical many exercise equipment manufacturers have plane performed from a standing position on developed various types of devices employing a force plate. isometrics and isokinetics. When considered as a 15. Vertical Push-Up. A push-up executed by the separate entity, force is only one factor influ- arms pressing off of a force plate in the ver- encing successful athletic performance. Unfor- tical plane from a stationary position in tunately, these isometric and isokinetic devices which the arms are fully extended. inhibit the natural movement patterns of accelera- The previously cited research and equipment tion and deceleration. were performed with "tools" which lack in- The three factors underlying all athletic perfor- telligence. That means the equipment was mance are: "unaware" that a subject was performing an exer- 1. Force cise on it. For example, the equipment employed 2. Displacement in the study conducted by Pipes and Wilmore 3. Duration of movement. assumed certain velocities on the isokinetic modality used. However, verification of the speed In all motor skills. muscular forces interact to was impossible since a closed loop feedback and move the body parts through the activity. The sensors were not used as they do not exist on the displacement of the body parts and the~rspeed of equipment employed. However, with the advent of motion are Important in the coord~nat~onof the ac- miniaturized electronics in computers, it IS possi- tivity and are also directly related to the forces ble today to join exercise equipment with the produced. However. it is only because of the con- computer's artificial intelligence. trol provided by the brain that the muscular forces Another important consideration in both the follow any particular displacement pattern. and design of equipment and the performance of an without these brain controls, there would be no athlete or a busy executive is that the human body skilled athletic performances. In every planned relies on preprogrammed activity by the central human motion, the intricate timing of the varying nervous system. This control necessitates exact forces is a critical factor in successful pertor- precision in the timing and coordination of both mances. the system of muscle contraction and the In any athletic performance. the accurate coor- segmental sequence of muscular activity. dination of the body parts and their velocities is Research has shown that a characteristic pattern essential for maximizing performances. This of motion is present during any intentional move- means that the generated muscular forces must ment of body segments against resistance. This occur at the right time for optimum results. For pattern consists of reciprocally organized activity this reason, the strongest weight lifter cannot put between the agonist and antagonist. These the shot as far as the experienced shotputter. reciprocal activities occur in consistent temporal Although the weight lifter possesses greater relationships with the motion parameters, such as muscular force, he has not trained his brain velocity, acceleration, and forces. centers to produce the correct forces at the ap- Hellebrandt and Houtz (488) shed some light propriate time. on the mechanism of muscle training in an ex- Neurological research has demonstrated that perimental demonstration of the overload princi- the brain performs differently depending upon ple. They found that repetition of contractions whether the desired motion is slow or fast. It was which place little stress on the neuromuscular found that the motor control centers reacted in system had little effect on the functional capacity one manner when slow andlor steady forces were of the skeletal muscles; however, they found that required, but reacted quite differently when the amount of work done per unit of time is the variable or quick forces were desired. Results critical variable upon which extension of the showed that control signals from the brain are limits of performance depends. The speed with more closely related to rate of change than to which functional capacity increases suggests force levels and, for this reason, the range and the that the central nervous system, as well as the speed of the exercise have important carry-over contractile tissue, is an important contributing implications for skilled athletic performance. In component of training. athletic events, the intricate timing of the varying In addition to the control by the nervous forces is a critical factor in successful perfor- system, the human body is composed of linked mances, and, therefore, training an isolated mus- segments, and rotation of these segments about cle group slowly may result in poorer athletic per- their anatomical axes is caused by force. Both formances. 297 In characterizing the movements of an athlete, Although prior to the early sixties there was the description is not of the independent contrac- very little work done in this area, McQueen (64) in tion of hundreds of thousands of muscle fibers, 1954 distinguished between exercise regimens but instead the particular activity is specified: for producing muscle l~ypertrophyand those for throwing, running, jumping, blocking, etc. All producing muscle power. He concluded that the athletic movements result from contractions of number of repetitions for each set of exercise muscles and the synergists in relative standard determines the different characteristics of the ex- patterns of coordinated activity. Therefore, ercise. Based on that evidence, Berger flooded research in exercise machine design should view the research literature in an attempt to find the op- the problem of motor control in terms of the se- timal combination of sets and repetitions for the quencing and coordination of agonists and an- gain of muscular strength (11-20). Berger used a tagonists. Ballistic motion results from properly one repetition maximum (1-RM)as his criterion for timed contractions of muscles integrating all of strength gain and had groups train at two, four, the joints involved in the activity. Because most six, eight, ten, and twelve repetitions maximum athletic events are ballistic movements and since for each set. His findings revealed that three sets the neural control of these patterns differs from of four to eight repetitions for three times per slow controlled movements, it is essential that week was the optimum training schedule for pro- training routines employ programmable motions ducing strength gains. The study also showed to suit specific movements. that training with two repetitions was better than training with 10-12 repetitions, which suggests EXERCISING METHODS that the closer the subject works to his 1-RM, the There is a significant difference between greater the strength gains. Other research by isotonic and isokinetic exercises. In lsotonic exer- Steinhause (86) emphasized the need to increase cises the inertia. that is, the initial resistance. has the intensity rather than the amount of work In to be overcome first and then the execution of the order to develop maximum strength. movement progresses. The we~ght of the resistance can not be heavier than the maximum In constant resistance training, if more than strength of the weakest muscle acting in a par- one repetition is to be used, one must use sub- ticular movement, or else the movement cannot maximal overload on the initial contractions in be completed. Consequently the amount of force order to complete the required repetitions. Other- generated by the muscles during an isotonic con- wise, the entire regimen will not be completed traction does not maintain maximum tension due to fatigue. Berger and Hardage (19) studied throughout the entire range of motion. In an this problem by training two groups of men with isokinetically loaded muscle, the desired speed of 10-RM. One group trained following the standard movement occurs almost immediately and the Berger technique while the other group used one muscle is able to generate a maximal force under repetition maximum for each of the ten repeti- a controlled and specifically selected speed of tions. This was accomplished by progressively contraction. The use of the isokinetic principle for reducing the weight for the next repetition in a overloading muscles to attain their maximal manner which paralleled the fatigue of the mus- power output have direct applications in the fields cle. The results showed that the intensity of the of sports medicine and athletic training. work seemed to be the important factor in Many rehabilitation programs utilize isokinetic strength increases, since the maximal overload training to recondition injured limbs to their full group showed significantly greater strength gains range of motion. Many athletes now train with than did the standard lORM group. "isokinetic equipment" to develop a muscle's Based on these findings it would seem ap- maximum power output capacity at a speed of propriate to assume that a modality which can ad- contraction similar to that required in their par- just the resistance so that it parallels fatigue to ticular performance. The unfortunate drawback to allow the maximum RM for each repetition would this type of training is that the speed is constant be superior to the currently available equipment. and there are no athletic activities which are per- Berger accomplished this function by removing formed at a constant velocity. weight from the bar while the subject trained. This is neither the most convenient nor the most Drac- Isotonic Exercise tical me!thod. Wit h the aid of the nqodern cc 3m- In 1945 Delorm (34) made one of the first at- puter, this functior1 can be performed automat i~cal- tempts to study dynamic resistance training (isotonic) and in 1948 again with Watkins (34, 35), l~. they introduced the conce~tof ~roaressive Variable nesrstance txercrs- resist2ince exerc 2ise (PRE:). ~hi'sco ncept rnv olved Another problem with constant resistance (the three :;ets of lift ing, each based on the amoi~nt of resistance load is constant, however with the aid weigh!t that can Ibe lifted n o more than ten tirr~es or of inertia due to the motion the problem is even ten re1petitions maximumI (10RM). Since th~! pro- more complicated), is not only maximal overload gram is- DaseaL---A on- _ rneIL_ progresswe------. . - reslsrance- --.-A _--_ pnn- per repetition but also overload throughout the ciple, the lORM must be adjusted periodicaIly as range of joint motiion. Since! overload on the mus- strength gains occur. cle chan!jes due tc ) both bio~mechanic al levers and the length tens~oncurve, the muscle can only ob- more important question for future consideration tain maximal overload in a small portion of the is to determine the carry over effect of different range of motion (8, 88). To overcome this short- types of training on independent testing of coming of constant resistance training, several strength, power, and speed of movement. companies (Universal, Nautilus and others) have manufactured strength training devices which Accommodating Resistance Exercise have "variable resistance" mechanisms in them. One of the newest developments in strength Variable resistance uses pulley and cam systems training and probably one which has been in- or combinations of levers to attempt to change vestigated most is isokinetics. lsokinetic simply means the same or constant motion. lsokinetic the resistance lever arm. The objective is that when the skeletal system is at its greatest disad- exercise is a form of isotonic exercise with one vantage, the equipment's load is the lightest, and major difference. By accommodating the when the skeletal system is at its greatest advan- resistance against a lever moving at a fixed veloci- tage, the machine's weight Is the heaviest for the ty, it allows continuous exercise with maximal muscle. dynamic overload throughout the entire range of Actually the Universal and the Nautilus motion. Therefore, isokinetics truly provides an systems increase the resistance in a linear "accommodating resistance" at a specific veloci- fashion but this linearity does not truly accom- ty (23,28,51,73,88). modate the individual. Also, individuals differ and, lsokinet~cshas received a great deal of clinical therefore, the variable constant of the existing application (10. 23, 28, 46, 48, 70, 83) but applica- machines only attempts to accommodate the tions in training studies are somewhat limited. In resistance. If one includes consideration of iner- 1967, Thistle et al. (88) compared isotonic and tial forces, then the accommodating resistance isometric training and found that after eight might be cancelled by the velocity of the move- weeks, the isokinetic group gained 35 percent in ment. Thus, the term "variable resistance" is more total work output, while the isotonic and the appropriate than accommodating resistance. isometric groups gained 27.5 and 9.4 percent. Very little research exists comparing variable respectively. In a similar study, Moffroid et al. (66) resistance exercise with other conventional found that isokinetic and isometric methods of strength training programs. A few studies by Ariel training produced greater strength gains than (4-7) compared the Universal dynamic variable isotonic training after four weeks of exercise. resistance (DVR) with conventional Olymp~c Pipes and Wilmore (75) conducted a study in barbells and revealed the superiority of the DVR 1975 comparing isokinetic and isotonic training. machine as far as both the rate of improvement of Thirty-six men were trained for eight weeks in one strength and absolute strength gains. A study by of four types of exercise: isotonic. slow isokinetic Plpes (76), also comparing DVR training with con- (24 deglsec), fast isokinetic (136 deglseg) and a stant resistance (CR) training, demonstrated control group. Strength was measured both strength increases for both groups but emphasiz- isotonically and isokinetically in addition to five ed that the relative increases were dependent on- performance variables and body composition the method in which relative strength was assess- measurements before and after training. They ed (i.e. DVR versus CR procedures). Pipes sug- concluded that fast speed isokinetic was superior gested that improvement should be the greatest to both isotonic and slow speed isotonic on when tested with the device or procedure that ap- strength and performance criteria. It should be proximated the training procedure. That means noted that the accuracy of this study has been specificity of training. In other words, if a person questioned by Berger and Wilmore. Thus, this trains fast and tests slow, he might not study must be viewed with caution until further demonstrate the same level of progress as if he research can substantiate these findings. were to both train and test at the same speed. This Several studies have compared isokinetic phenomenon is extremely important since the ef- training at different velocities to determine the ef- fects of carry over training to performance are pro- fect of the amount of work done and the rate at bably interdependent. For example, if a javelin which the work was performed (10,60,65,66). The thrower wants to improve his throwing capability findings of these training velocity studies sum- by increasing his strength, he should train on a marized by Moffroid et al. (65) in 1970 are as modality which allows the speed of motion to be follows: comparable to his javelin throw. One of the 1. Low power (low speed, high load) exercise methods employed by the Eastern European produced greater increases in muscular countries in their athletic training programs is to force only at low speeds. assign the proper mode of training for each 2. High power (high speed, low load) exercise specific event. produced increases in force at all speeds of To date it appears that research has been contraction at and below the training speed. unable to demonstrate pronounced superiority of 3. High power exercise increased muscular en- any of-the training methods and a need exists for durance at high speeds more than low power cross-testing between training procedures and exercise was able to increase muscular en- equipment. In addition, it seems that an even durance at low speeds. Thus, the principle of specificity of training blem is the time lag associated with moving from was reinforced by showing that the amount of a zero velocity to the desired speed. Obviously the work done is not as important as the rate at which bar must begin to move from a 0 velocity and at it is performed (65). Moffroid's conclusions, some point attains the des~redvelocity; however, however, do not agree with a recent study by the question is how long is required to accelerate Krokiewski et al., who trained a group of 10 tne bar until it reaches this velocity? Additional women for five weeks isokinetically (60 deglsec). difficulties are: Krokiewski's results showed strength gains at all 1. that the isokinetic machine does not hold a velocities (0,30,60,120, and 180 deglsec). constant velocity Rosentsweig et al. (81) compared isometric, 2. that it is possible to accelerate the bar up to isotonic, and isokinetic exercise by elec- 35 percent near the end of the movement. tromyography. They concluded that isotonic ac- tivity and isokinetic exercise produced more Because of these problems, most of the muscular electrical activity than was elicited by research performed to date can properly be isometric exercise. However, there was no dif- challenged since the assumptions do not appear ference in the muscular electrical activity to be valid. generated when isokinetic and isotonic exercises Additional considerations include the changes were compared. in inertia and velocity which accomDany the varia- Some of the basic and most frequently used, tion in the body segments themselves and the weight training methods for improving muscular variations among individuals, lnman and Ralston strength are described as follows: (54A) in 1954 pointed out some of these variations. They described one important variation in the 1. DeLorme classic work: following way: 1 set of 10 reps., with 1/2 lORM An interesting observation on the human 1 set of 10 reps., with 3h 10RM skeletal lever system is that by maximum 1 set of 10 reps., with lORM muscle effort, relatively constant moments 2. Berger method: are produced agalnst resistance no matter 1 set of 8 reps., with 8RM what the angular position of the articulating 1 set of 6 reps., with 6RM segment. This IS surprising since the lever 1 set of 4 reps., with 4RM arms through which the muscles act vary 3. "Oxford" method: continuously with changing position of the 1 set of 10 reps., with 100% 10RM part. To produce such an effect 1 set of 10 reps., with 90% 10RM necessitates a varying force to compensate 1 set of 10 reps., with 80% 10RM for the varying lever arm, and such a 4. The "German Pyramid": mechanism IS actually found in the muscle itself. In the body. therefore. is a 1 set of isometric contraction reci~rocatingarrangement of muscles and 1 set of 1 rep.. with 100% 1RM levers by which changing lengths of lever 1 set of 2 reps., with 90% 1RM arms are offset by changes in the ability of 1 set of 3 reps., with 80% 1RM the muscles to develop torques about the 1 set of 4 reps., with 70% 1RM joints. The nicety of the compensatory rela- 1 set of 5 reps., with 60% 1RM t~onshipand the physiology of muscle con- 1 set of 4 reps., with 70% 1RM traction has not been fully appreciated. 1 set of 3 reps., with 80% 1RM This is a description of the compensatory in- 1 set of 2 reps., with 90% 1RM teraction between the length-tension curve and There seem to be unlimited methods and each the leverage system in normal movement without system is supported and refuted by as many "ex- great resistance being applied to the body seg- perts". In the past, the problem of validly ment. However, when great resistance is applied evaluating the different modes of exercise was to the body segment, the length-tension rendered impossible because of the lack of the phenomenon changes dramatically by the addi- proper diagnostic tools. For example, in the tional load and the investigator must be aware of isotonic type of exercise the investigator does not these changes and be able to quantify the know exactly the muscular effort and the speed of changes. Without such considerations, his movement but knows only the weight which has research is worthless. been lifted. When a static weight is lifted the force The concept of strength variation through the of inertia is a significant contribution to the load range of joint motion presents a broader concept and cannot be quantified by feel or observation of muscular force development. A question alone. In the isokinetic mode, the calibration of should be raised regarding the extent to which the velocity is assumed and has been very poorly muscle training is efficient when performed with a verified. The rotation of a dial to a specific loca- regular barbell or on equipment designed without tion does not guarantee the accuracy of valid scientific bases. Functional movements are subsequently generated velocity. In fact, frequently ballistic in nature, and the relationship discrepancies as great as 40 percent are found of joint moment measurements to dynamic or when verifying the velocity of the bar. Another pro- phasic activity needs to be considered when designing exercise equipment when the goal of novative features and mechanisms to the long- that equipment is to facilitate efficient muscular established fields of resistive exercise or training strength development. Not only do force values for athletics, rehabilitation, and physical fitness. vary among muscle groups but the rotational ef- The underlying principle behind these innovations fect of a given group depends on the position of is that of a computer controlled feedback or servo- the joint it moves. mechanism which is able to maintain any desired pattern of force and motion throughout the range Problems to Avoid in Equipment Design of each exercise, regardless of the magnitude or In weight training for sports activities or for rate of force applied by the person exercising. The rehabilitation. the ultimate objective is for the advantages of an intelligent feedback-controlled muscle to function at maximum efficiency mechanism over existing resistive exercise throughout the range of movement. These objec- mechanisms are many. tives necessitate proper assignment of force, First, all systems which employ weights as the displacement, and velocity, as well as when mechanism for resistance have major drawbacks desired, time, acceleration, the amount of work, in four or more areas: and power. To accomplish this objective, it is necessary to assess man's biomechanical 1. biomechanical considerations changes and then develop a resistance and veloci- 2. inertia ty intensity that will accommodate those changes 3. risk of injury in a functional manner. The variations in 4. uni-directional resistance. resistance intensity and velocity must be precise- The biomechanical considerations are the ly incorporated into an intelligent resistance lif- most important for exercise equipment and have ting mechanism. It is likewise essential that the been previously explained. Inertia is the property entire machine design and operation do not of resisting any change in motion and, because of adversely affect the performance of this this property. it requires a greater force to begin mechanism. moving weights than it does to keep them movtng To prevent both machine design and opera- in a constant manner. Similarly, when the person tional failures, it is necessary to understand the exercising slows his motion at the end of an exer- relative effects of inertia. Inertial forces affect the cise movement, the weights tend to keep moving motion and the magnitude of the muscle's in- until slowed by gravity. This phenomenon reduces volvement. The smaller the inertial force produced the required force at the end of a motion se- by the machine's moving parts, the greater the quence. This property becomes especially pro- muscular involvement. In order to maintain small nounced as acceleration and deceleration in- inertial forces, it is important to reta~nproper crease, effectively reducing the useful range of mechanical balances in the lifting ratios and allow motion of weight-based exercise equipment. The the machine to use its own intelltgence to control risk of injury is obvious in weight-based exercise the moving parts. Obviously, this control must be equipment. When weights are raised during the supplied by the micro-computer which senses the performance of an exercise, they must be lowered movement of the machine's parts. This inertia to their original resting position before the person controlled mechanism cannot be ignored in op- using the equipment can release the equipment timum equipment design. and stop exercising. Injury could easily result if the weights fell back to their resting position ac- THE INTELLIGENT EXERCISE MACHINE companied by the concomitant motion of the bar In all the previous descriptions of exerclse or the handle attached to the weights. If the per- equipment, the user has had to determine the son exercising happened to lose his grip, or was amount of resistance and the number of repeti- unable to hold the weights due to exhaustion or tions desired. The reason the user made the inbalance, serious injuries could and have choices was, of course, that the exercise equip- resulted. Finally, while being raised or lowered, ment itself was inherently incapable of any in- weights or exercise equipment employing tellectual participation. However, with the advent weights offer resistance only in the direction op- of computers, it became possible to design exer- posite to that of gravity. This resistance can be cise equipment with artificial intelligence enabl- redirected by pulleys and gears, but still remains ing the computerized machine to select the best uni-directional. In almost every exercise perform- exercise method based on each individual user. ed, the muscle or muscles being trained by The original concept was published by Ariel (4) in resistance in one direction are balanced by a cor- 1976. Thus, the user need not be an expert in any responding muscle or muscles that could be train- biological, physiology. or exercise area since the ed by resistance in the opposite direction. With exercise machine is programmed with informa- weight-based systems, a different exercise, and tion from many scientific fields thus, correctly often a different mechanism, are necessary to benefitting the different individual users. train these opposing muscles. The exercise machine described herein is the Exercise mechanisms which employ springs, result of the application of many unique, in- torsion bars, and the like are able to overcome the inertia problem of weight-based mechanisms and weight, and to have that resistance increased by can partially overcome the uni-directional force 10 percent in each successive repetition, until the restriction by both expanding and compressing user reaches a "sticking point" and cannot con- the springs. However, the serious problem of safe- tinue. With a classical weight machine, he would ty remains. An additional problem is the fixed, have to initially select weights equal to half his non-linear resistance which is characteristic of body weight, and then stop between each repeti- springs, and usually unacceptable to most users of exercise equipment. tion to change weights, with the probability that The third type of resistive mechanism com- he would not be able to select the desired unit of monly employed in existing exercise equipment is increase since weights are normally available in 5, that of a hydraulic mechanism. This mechanism is 10, 25, or 50 pound units only. In addition, the able to overcome the inertial problem of weights training effect of the exercise is considerably af- and the safety problem of both weights and spr- fected because, while he stops to change ings. With the appropriate selection or configura- weights, his muscles "recover". If. with the tion of hydraulic mechanisms, the uni-directional lsokinetic or other devices, there were a force problem can also be overcome. However, previous readout (which is not included on any of the cur- applications of the hydraulic principle have rently available equipment), the user would have demonstrated a serious deficiency that has to watch that readout and match the force pulled limited their popularlity in resistive training. This with the desired force as it appeared on the deficiency is that of a fixed (although perhaps readout. nhis is analogous to trying to keep the preselected) flow rate through the hydraulic high performance race "car" on the "road" in the system. With a fixed flow rate, it is a well- video arcade games.) This would require more established fact that resistance is a function of control and concentration than most persons are the velocity of the piston, and in fact, varies quite capable of especially with the onset of exercise- rapidly with changes in velocity. it becomes dif- induced fatigue. With the Computer~zedExerclse ficult for the person exercising to select a given Machine, the person's weight woula automatically resistance to train with since he is usually con- be determ~nedby having him support himself strained to moving either slower or faster than he briefly on the exercise bar. Then the computer would like in order to maintain this resistance. Ad- would select the pattern of increasing force, star- ditionally. at any given moment, the user is unsure ting at precisely half his body weight, and increas- of just what his performing force or velocity ac- ing the resistance by just 10 percent after each tually is. For these reasons. hydraulic repetition until it detected that the user could no mechanisms have found only limited acceptance longer move the bar. At this polnt. it would report among serious users of exercise equipment. the final force level. the number of repetitions, and, if desired, the progress the user had made Feedback Control of Exercise since the last exercise session. The Ariel Computerized Exercise Machine A second example is that of a user desiring to possesses several unique advances over other exercise with a constant force or a predeterm~ned resistive exercise mechanisms, both fixed and force pattern fi.e. non-linear force through the feedback-controlled. The most significant of range of motion). In addit~on,at the point in the these advances is the introduction of a stored- range of motion where his speed is the lowest (his program computer to the feedback loop. The com- weakest point). the user may want the bar to puter, and its associated collection of unique pro- "lock" for three seconds so that strength could be grams, allows the feedback-controlled resistance enhanced through isometric rather than isotonic to vary not only with the measured parameters of exercise. After the three second isometric con- force and displacement, but additionally, to traction, the motion would be allowed to continue modify that feedback loop while the exercise is in through the next cycle until this sticking point progress. This modification can, therefore, reflect would again be encountered. Experts in various changes in the pattern of exercise over time. The professions believe that such an exercise is a vast unique program selection can effect such improvement over conventional resistive training changes in order to achieve a sequential or pat- for developing strength at a person's weakest terned progression of resistance for optimum points. Yet it would be impossible for this exer- training effect. The advantage of this capability cise to be performed on any other exercise over previous systems is that the user can select machine known to exist. Not only can the propos- the overall pattern of exercise and the machine ed exercise system perform this pattern of exer- assumes responsibility for choosing the precise cise, but during and after the exercise it can force level, speed of movement, and temporal se- display the level of strength at the "sticking quence to achieve that pattern. point" and how this compares both to previous Consider the following typical examples of ex- strength levels and to the strength over the entire ercises which can be performed on this machine range of motion. In addition, the programs are which would be impossible on any other exercise then able to adjust ensuing exercise sessions to machine. A user wishes to select a resistance select the proper range of forces to continue to (weight, in classical terms) starting at l/2 his body build strength, based on the progress to date. All of this is accomplished without the user having to ankles, shoulders, etc., between or under pads at- remember or reenter any data. tached to the moveable bar. The exercise consists of alternately pulling and pushing on the bar (or Description of the Computerized Exercise any handle-like attachments) so that the bar pivots Machine about its point of attachment in alternate direc- The computerized exercise machine consists tions. As the bar pivots, the attached cylinder rod of the following arrangement of components: moves the hydraulic piston up or down depending Two-way, single-rod-endhydraulic cylinder. upon the direction of the exercise. As the Rotary hydrauling spool valve for control ling hydraulic piston moves, fluid is forced out of one the flow of fluid through the hydraulic end of the cylinder, through the appropriate check system. values, through the rotary spool valve, and back in- DC stepper motor (bi-directional) for turning to the opposite end of the cylinder. Fluid is hydraulic valve. shunted to and from the make-up reservoir on the Hydraulic connector block, used to connect low-pressure side of the spool valve to accom- various hydraulic components in the proper modate the change in volume in the cylinder as configuration. the rod moves in and out. This reservoir is Hydraulic check valves to permit flow of fluid pressurized to avoid cavitation on the low in one direction only. pressure side of the piston during rapid move- Pressurized fluid reservoir, to accommodate ment of the rod. Fluid pressure on the high fluid volume changes due to movement of pressure side of the spool valve is continuously single-rod-endcylinder. monitored and, since the area of the piston is Brackets for attaching cylinder assembly to known, the force on the rod is continuously frame and bar. calculated by the computer. Similarly the angular Supporting frame for exercise machines. displacement of the bar is continuously The bar is assembled in such a way that it monitored by comparing the voltage output of the pivoted at the frame and attached at a point potentiometer with the reference voltage at the along its length to the rod of the hydraulic limits of excursion. In addition, velocity and ac- cylinder. Movement of the free end of this bar celeration of the bar are also computed on a con- causes the piston to move in the hydraulic tinuous basis based on sequential readings of cylinder. displacement measured against the precision Detachable handles, pads, plates, etc. as real-timeclock in the computer. means to interface moveable bar to the user. With the spool valve full open the bar freely Pressure transducer for measuring force on moves up and down with only a small amount of the hydraulic piston through a measurement resistance due to the sliding friction of the of the hydraulic fluid pressure. hydraulic cylinder. As the spool valve is closed. Angular displacement transducer, conslsting there is increasing resistance to the flow of of a potentiometer coupled to the rotating hydraulic fluid in the system, and, therefore, in- pivot shaft of the bar. creasing resistance to moving the cylinder rod AID converter for translating voltage levels and the bar attached to it. At the full closed posi- from the transducers (numbers 11 and 12 tion of the valve, the cylinder cannot be moved, above) to digital values readable by the com- and the bar is locked in position. Due to the con- puter. struction of the cylinder. and the appropriate ar- Stepper motor driver, for converter digital rangement of the check valves, this system yields pulses from the computer to the proper a resistance in either direction of motion. Further- power switching sequence for driving the more, the direction of motion may be reversed at stepper motor in the forward or reverse direc- any time without the mechanism having to change tions. modes or configuration. other than perhaps an ad- Stepper motor power supply. justment of the spool valve to yield the ap- Computer: Consisting of central processing propriate resistance for the given direction of mo- unit, internal memory, multiple display inter- tion. face, printer interface, AID converter inter- The computer controlled feedback function of face, digital output interface, extended this exercise machine can be illustrated by the secondary memory (disks), appropriate following example: Utilizing the display, the com- power supplies, and cabinet or housing. puter presents a menu of available exercise func- Color graphics display. tions. Using the keyboard, the user selects for the Keyboard for display. upstroke a linearly decreasing force starting at Light pen for display. 100 and ending at 50 pounds. He then selects a Line printer. constant force of 60 pounds for the downstroke. The computer now calculates the intermediate Functional Description force levels for the intervening positions from bot- A user of this exercise machine positions tom to top to give a linearly decreasing force himself (standing, sitting, lying down) so that he between the limits given, and then informs the may grasp the handles, or position his wrists. user to begin exercising. The initial position of the bar is unimportant since the computer measures 2. locking the bar if the excursion is exceeded the current position of the bar, the direction of 3. sounding the display's audible alarm with an movement, and sets the resistance accordingly. appropriate message andlor printed on the Assuming that the user starts at the bottom of the display stroke, and begins moving upward, the following 4. even ignoring the limits and letting the user process occurs. Initially, the computer closes the exercise as he pleases, with perhaps a report spool valve to prevent the bar from moving. The afterward on his range of motion. user pulls upward on the bar until the internal fluid Since constant force is desired, position of the pressure reaches a value that corresponds to 100 bar is unimportant. Feedback is based on the pounds on the handle. At this point, the computer pressure measurement alone, and again, the com- opens the valve permitting the bar to begin mov- puter will open or close the valve to maintain the ing slightly. As the bar moves, the computer con- desired force on the handle. When the user again tinuously senses force (pressure) and position. At changes directions, the upstroke force pattern is each position, it compares the measured force on again selected, and this process continues for the the bar with the desired force. For example. number of repetitions selected (Repetition selec- assume the bar has moved two degrees and the tion may be automatically selected by the com- force, as precalculated, should now be 98 pounds. puter, manually by the user, or the user may exer- If the user is still pulling with 100 pounds, the cise with no repetition limit). During the exercise, valve is opened a small amount. If the user is still the display will show the current and desired pulling with 100 pounds, the valve is opened a number of repetitions, the velocity, andlor any small amount. If the user is only pulling with 96 number of other parameters that the user may pounds, the valve is closed a small amount and have selected to be alsplayed prior to his beg~n- the cycle repeats. As the user raises the bar to the ning the exercise session. upper position, the computer continues to reduce The user could have alternately selected a the force on the bar with the appropriate ad- velocrty as a function of position of the bar. rather justments of the valve. Note that it is not impor- than a force. and the computer could have maln- tant how fast the user moves the bar. If he wlshes talned such a pattern. In this mode, force on the to move the bar slowly, the valve is closed to main- handle would not be used in the feedback loop tain the desired force. If he wishes to increase the (although it would be measured and, optionally. speed of movement of the bar, the valve is opened saved and reported). Rather, the continuously to accommodate the greater flow while still main- computed bar velocity would be compared to the tain~ngthe desired force. The feedback nature of desired velocity. If the actual velocity were low. the mechanism allows this performance flexibility the valve would be stepped open siightly, and if since force and position are continuously high, the valve would be stepped closed slightly. monitored and compared to expected force at the This cycle would be repeated throughout the same position, with appropriate adjustment of the range of motion to maintain the desired move- valve if the force is high or low. The computerized ment pattern. It is now only a simple extension to "intelligence" of the machine provides the combine force andlor velocity selection into more capability to "expect" a force and velocity and is complex patterns, perha~sincluding acceleration one of the unique features of this machine. or other time-related patterns (such as locking the The user now changes directions and begins bar for three seconds at some particular po~nt, the downstroke. If the user did not complete, or then continuing in the desired mode). With the exceeded the upstroke, several options are control afforded by the computer, there is no limit available under computer control, and may be to the number or type of exercises that can be per- preselected by the user, including: formed. 1. locking the bar in the opposite direction if in- complete

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