RESNA 27th International Annual Confence
The Feasibility Of Measuring Keyboard Forces During A Typing Task To Determine The Efficacy Of Physical Therapy On Patients With Known Musculoskeletal Hand And Wrist Disorders
The Feasibility Of Measuring Keyboard Forces During A Typing Task To Determine The Efficacy
This action research evaluated the effectiveness of using a force sensitive platform apparatus to measure the pre and post therapy forces applied to a keyboard during a typing transcription task. Such an apparatus could be used to determine the efficacy of physical therapy on patients that have hand and/or wrist musculoskeletal disorders. In addition to force, other variables such as Inter Keystroke Intervals (IKI) and typing transcription accuracy was measured to further evaluate the performance and progress of a patient. This study quantified the aforementioned measures of keyboard force, IKI and accuracy during a typing transcription task. However the marginal documented differences of the pre and post-physical therapy measures suggest that the apparatus should be used with other objective and subjective measures to improve its validity as a diagnostic tool for determining the efficacy of physical therapy and or the performance of an individual in a typing task scenario.
Keyboard forces; hand and wrist musculoskeletal disorders; physical therapy efficacy
Researchers have looked at the relationship of timing and force and have speculated that in preparing a movement both time and force must be specified before the response is released and before another timing cycle begins (1). Keele et al, (1) suggested that factors of force control and timing control are largely, but not entirely, independent. Force and time appear to have a modest interaction in both peripheral and central stages of motor production. To measure and understand applied forces, timing and posture during a typing task, researchers have used a variety of apparatus and test instruments. Young and Barton (2) developed a force-sensitive platform used in conjunction with a minicomputer to measure and record behavior of people pressing keys on a device, such as a calculator or computer keyboard. Their force platform fulfilled its primary purpose of recording the force identity and timing of an operator's key press.
Thomas Armstrong et al, at the University of Michigan developed an objective keystroke force measuring apparatus and found that peak forces at each keystroke were 2.5 to 3.9 times the minimum required key activation forces on a computer keyboard (3). Their finding suggests that participants consistently displaced the keys to their limits and beyond. Another study at the University of Michigan determined that the overall mean peak reaction force during a typing task is 2.54 Newtons (263.1 grams), which is 5.4 times the minimum key actuation make-force of .47 Newtons (47.6 grams) (4). Rose (5) indicated that finger force was increased with a thin film keyboard, and increased muscle tension was realized to avoid accidental key activation. This study suggests that the key actuation force needs to be greater than the finger weight. To accommodate a mean relaxed finger weight, a .50 (50.6 grams) Newton key activation force would be required.
Another objective measure of the mechanical and physiological forces applied to an individual during a typing task is the electromyographic (EMG) output during typewriter and keyboard use. One study found that mechanical typewriters caused a higher and more dynamic strain on the forearm and finger muscles than did modern electronic keyboards (6). Dennerlein et al, (7) found that EMG activity for each keystroke followed a repeatable pattern, in that the EMG activity of the finger extensor increased before the finger rose and then decreased before and during the down swing. After finger impact there was a period of co-contraction of the flexors and extensors.
In terms of motor control of rapid-targeted movements, ballistic movement incorporates agonist and antagonist muscle systems. The agonist muscle initiates the movement and the antagonist muscle stops or brakes the movement. During the down swing movement of a keystroke the extensors, (the antagonists), are not active; their EMG output decreases after lifting the finger and then becomes active again after finger impact. Hence, the extensor EMG follows a ballistic pattern of movements against a stop. The role of the flexor is assumed to initiate the downward movement. Gravity, tissue elasticity and/or more remote muscles may also propel the initial downward force of the finger. Dennerlein et al, (7) concluded that the control of finger motion during typing appears to be a ballistic movement, except in the sense of the role of the flexor (agonist) muscles initiating the movement.
The objective of this action research was to explore the feasibility of measuring keyboard forces during a typing task to determine the efficacy of physical therapy on a patient. The patient who participated in this pilot study had a musculoskeletal hand and wrist disorder that required physical therapy.
Peak keystroke forces were measured using a force-sensitive platform apparatus that incorporated a calibrated pair of Omega platform load cells. The computer keyboard was centered on the apparatus approximately two inches from each end of the platform. Each load cell was calibrated separately using certified weights that ranged from 50g to 1000g. The resultant calibration curve was linear thus validating the load cell signals. The load cell signals were amplified using two Sensotec signal conditioner indicators. The conditioned (amplified) load cell signal was then sampled at 100 Hz (10 msec) and recorded by a Measuring Computing Corp. analog to digital board that was placed in a Gateway 486 computer. The digital signal was than formatted by custom designed software that identified the key that was being activated, the force required to activate the key and when the key was activated.
One participant with known musculoskeletal disorder was tested. This test required that the participant, prior to her initial physical therapy session and after her final physical therapy session, perform a four-minute typing task. To illustrate, the participant was instructed to transcribe a scripted text as fast and as accurately as she could, until the computer prompted her to stop. The same typing task was performed pre-physical therapy treatment as well as post-physical therapy treatment.
The female participant had realized a left wrist fracture and presently was being treated for tendonitis. Treatment consisted of prescribed ultra sound and wrist exercises. Over approximately a thirty-seven day period between the pretest and posttest the participant had received seven half hour (30 minute) physical therapy treatments.
The pre and post-therapy peak keystroke forces were measured and configured to identify the number of key characters typed, as well as individual keystroke forces associated with those characters during the four minute typing task. The mean was than calculated for the peak keystroke force and the Inter Keystroke Interval (IKI). In addition to documenting keystroke force and IKI, typing transcription errors were documented to evaluate participant accuracy.
The pre and post therapy character counts for the number of characters made in the four minute typing tasks show that there was a 2.5 percent reduction in the number of characters made in the post therapy test to the pre therapy test. These character count of 1258 equates to a mean of 190 millisecond IKI for the post therapy test, and the character count of 1291 equates to a mean of 185 millisecond IKI for the pre-therapy test.
The pre and post therapy means grams (g) of force in the four minute typing tasks show that there was a 5.0 percent increase in the mean forces applied in the post-therapy test compared to the pre-therapy test. This equates to 17.7 more mean peak keystroke grams of force being applied to the keyboard in the post therapy test than the pre therapy test.
Concerning typing accuracy there was more typing transcription errors in the post therapy test than the pre therapy test. To illustrate the participant typed 2.6 percent fewer characters in the post therapy test, yet she had 8.3 percent more errors than the pre test. These errors consisted of transposed characters, character omissions, word and word spacing duplications.
From this action research it is questionable if the analysis of keystroke force alone can determine the efficacy of physical therapy on a patient with a known musculoskeletal hand or wrist disorder. As outlined in this pilot study, there was a marginal increase of approximately 5.0 percent in the keystroke force, and a 2.5 percent reduction in the Inter Keystroke Interval after physical therapy. Because of the limited number of participants it is questionable if such percentage differences would be statistically significant enough to answer the research question of similar studies.
However it should be recognized that if multi-objective analysis included typing speed, keystroke force, accuracy and other objective measures such as electromyographic (EMG) output during typewriter and keyboard use they could collectively yield statistically significant results in a multivariate analysis. These objective measures could and should be combined with subjective pain measures to further validate the internal and external validity, as well as statistical conclusion validity.
The results of this pilot study illustrate the usefulness, and the limitations of a keyboard force sensitive platform to measure the efficacy of physical therapy on patients with hand and wrist musculoskeletal disorders. For example, the hardware associated with force sensitive platform apparatus coupled with the custom software has accurately measured the force applied to a keyboard, the typing rate or speed of a participant, as well as identifying the keys that are being struck or activated. Subsequently the apparatus can be an effective objective measure, however it should be used with other objective and subjective measures to improve its validity as a diagnostic tool for determining the efficacy of physical therapy and or the performance of an individual in a typing task scenario. Further work in this area should include other subjective and objective measures with the force sensitive platform, as well as the use of more participants in targeted and general populations to further develop a comprehensive tool that could be used for diagnostic purposes.
Mark A. Koch, (ABD) Ph.D.
University of South Dakota,
Vermillion SD, 57069
Office Phone 605-362-8910,