Industrial ERG

CHAPTER 8 Psychophysics

LEARNING OBJECTIVE

This chapter will provide a discussion of psychophysics.

The learning objectives for this chapter are as follows:

· Understanding the origins of psychophysics

· How to conduct a psychophysical study

· How to use a psychophysical scale.

INTRODUCTION

On a Sunday, Bob participated in a marathon and then celebrated well into evening for finishing the race in the top 100. It is now Monday morning and he is supposed to perform 100% at his job as a loading dock worker. How might he perform? At 100%, 70%, or might he be exhausted? Many things play into how he might perform. Does he have physical issues because of the marathon or the partying afterward or does he feel motivated because he did so well in the marathon and had an enjoyable evening? Performance at work is not always based on the condition of the body, but also on how the mind controls the body. Psychophysics is the study of how the mind and body work together to perform a task.

Psychophysics is most commonly defined as the quantitative branch of the study of perception. Psychophysics examines the relations between observed stimuli and responses and the reasons for those relations. This definition is a very narrow view of the influence this branch of psychology has had on much of psychology in general. Psychophysics has been based on the assumption that the human perceptual system is a measuring instrument yielding results such as experiences, judgments, and responses that may be systematically analyzed. Psychophysics has a relatively long history of over 140 years, and its experimental methods, data analyses, and models of underlying perceptual and cognitive processes have reached a high level of refinement. Because of this, many of the techniques originally developed in psychophysics have been used to unravel problems in learning, memory, attitude measurement, social psychology, and, most importantly, ergonomics. Scaling and measurement theory have adapted psychophysical methods and models to analyze decision making in contexts entirely divorced from perception.

Psychophysics is an old branch of psychology that is concerned with the relationship between sensations and their physical stimuli (Snook, 1978). Modern psychophysical theory states that the strength of a sensation (S) is directly related to the intensity of its physical stimulus (I) by means of a power function: “S = KI”. The constant (K) is a function of the particular units of measurement that are used. When plotted on log-log coordinates, a power function is represented as a straight line. Many exponents have been determined for various types of stimuli (NIOSH, 1981). Some of these are electric shock, 3.5; taste, 1.3; and loudness, 0.6. Stevens (1976) suggested that for lifting the exponent was 1.45. In a recent study, Baxter, Stalhammer, and Troup (Baxter, 1986) studied the Stevens' power function for the heaviness of boxes being lifted and lowered. This was determined for 91 firemen by using a ratio rating method. For 90/91 subjects, the equation was satisfactorily fitted to a power relationship despite considerable variation between individuals. The mean exponent for perceived heaviness was 1.35 and fractionation point 0.06 kg (fractionation being the k or constant). The authors concluded that doubling a weight being lifted resulted in a 2.6 increase in perceived weight.

Psychophysics has been applied to many areas. Psychophysics was used by Houghton and Yagloglou (1923) in the development of the effective temperature scale and by Stevens (1960) in the development of the scales of brightness. Foreman et al. (1984) applied acceptability scaling to vertical isometric force applications at knee and waist levels. Subjects were asked to select a comfortable level of force that they judged could be held for 2 min. This proved repeatable; however, subjects did express some difficulty in imagining the effort for that long of duration. Borg (1962, 1970) used psychophysics in the development of the ratings of perceived exertion (RPE scale). The current RPE scale, which was modified by Borg in 1970, is a scale consisting of 15 grades from 6 to 20 (see  Table 8.1 ). The number 7 represents a very, very light workload; the number 9 a very light workload; the number 11 a fairly light workload; the number 13 a somewhat heavy workload; the number 15 a heavy workload; the number 17 a very heavy workload; and the number 19 a very, very heavy workload. Elkblom and Goldberg (1971) found in many situations the subject's heart rate mirrors the physical strain experienced subjectively. That is, the rating of perceived exertion a subject gave a task multiplied by 10 approximated the subject's heart rate observed for that task.

Table 8.1  Borg's Rating of Perceived Exertion Scale

6	Very, very light
8
9	Very light
10
11	Fairly light
12
13	Somewhat heavy
14
15	Heavy
16
17	Very heavy
18
19	Very, very heavy
20	Maximal exertion

Source: Adapted from Borg (1970).

Davies and Sargent (1979), however, found that heart rate per se has little influence on RPE and is not an important factor underlying the perception of effort. The RPE scale has been used by numerous researchers in many areas of physical exertion and discomfort. Davies and White (1982) used the RPE scale to rate how subjects perceived their exertion while performing exercise running uphill, walking, and performing the box stepping test. The researchers found that the subjects' energy consumption and their rating of perceived exertion were well correlated. Nordin et al. (1984) studied the effect of the weight of paint on the workload of painters painting ceilings and found that all but one subject perceived their workload to be less with lighter paint. There were no significant differences in heart rate or total oxygen consumption between the paints, but oxygen consumption per area of ceiling painted was less. Although not specifically stated in the article, the data presented indicated that the rating of perceived exertion multiplied by 10 did not approximate heart rate. Balogun et al. (1986) used the RPE scale to determine the perceptual responses while carrying external loads on the head and by a yoke. The researchers defined two RPE scales. The first was the RPE-L or local rating of perceived exertion. This was used to determine the subjects' perception of exertion by the neck muscles while carrying loads on their head. The second scale was the RPE-0 scale or overall perception of perceived exertion. This was used to determine the subjects' overall perception of perceived exertion while performing a maximal exercise on a treadmill. In summary, the RPE has been proven to give good indications of subjects' perceived exertion while performing a wide variety of physical activities. Some of the first studies that utilized psychophysics in lifting were conducted by the U.S. Air Force (Emanuel et al., 1956; Switzer, 1962). The psychophysical approach to studying lifting varies from other approaches in that the subject has control of one of the task variables. This variable is usually the weight the subject is asked to lift. Before the experiment begins, the subject is instructed to lift as much as he or she can without overexertion or excessive fatigue. The weight they select to lift is referred to as the maximum acceptable weight of lift. Asfour (1980) instructed his subjects to adjust the load to the maximum amount they could lift without strain or discomfort, without being tired, weakened, overheated, or out of breath. Legg and Myles (1981) state that with good subject cooperation and firm experimental control, the psychophysical method can identify loads that subjects can lift repetitively for an 8-h workday without metabolic, cardiovascular, or subjective evidence of fatigue. Psychophysical lifting capacity studies have been conducted by Snook and Irvine (1967), Snook et al. (1970), McConville and Hertzberg (1966), Poulson (1970), McDaniel (1972), Dryden (1973), Knipfer (1974), Ayoub et al. (1978), Karwowski (1982) Bakken (1983), Mital (1983, 1986), Jiang (1984), Hafez (1984), Fernandez (1986), and others. Varied aspects of lifting have been studied, and many psychophysical lifting capacity prediction models have been developed. Ayoub et al. (1978) designed a study to develop predictive models for different height levels as a function of operator and task variables. The results from this study were used by Mital and Ayoub (1980) to develop lifting capacity models, which could accommodate varied paces of work. Karwowski (1982) conducted a study in which biomechanical and physiological stresses were measured simultaneously. He used the “fuzzy set” theory to develop a model that incorporated the interactions of those stresses in a moderate environment. Bakken (1983) studied the interaction of lifting range and frequency of lift. Hafez (1984) conducted a study to determine the effects of high heat levels, varied lifting frequencies, and their interaction on the ability to perform psychophysical work. Mital and Aghazadeh (1987) conducted a study to determine the acceptable weight of lift above reach height. The psychophysical approach is not above criticism, however. Garg & Ayoub (1980) observed that there was considerable disagreement among investigators in regard to the maximum acceptable weight of lift. Mital (1983) conducted an experiment to verify the psychophysical methodology used to determine the lifting capacity. The subjects estimated the load they could lift after a 26-min load adjustment period. The subjects then lifted for 8- and 12-h periods. On an average during the 8-h lifting session, males could only lift 65% of the weight they estimated during the load adjustment period. Females could only lift 84% of the weight they had estimated. During the 12-h session, male subjects only lifted 70% of the weight they had estimated and female subjects lifted only 77%. For the 12-h session, the male subjects selected a weight during the weight adjustment period that was considerably less than the weight selected for the 8-h session. Fernandez (1986) found the reduction for the 8-h period was an average of 86% of the weight the male subjects estimated they could lift. This study showed the difference to be much less than that Mital found. Ayoub and Selan (1983) stated that the psychophysical criterion is an appropriate single design criterion to use in the determination of lifting capacity. Inputs for psychophysical lifting prediction models include static and dynamic strength data, lifting frequency, and range of lift. The isoinertial incremental 6-ft lift strength test (6-ft lift) has been used as an input for many psychophysical lifting capacity models (Ayoub et al., 1986a,b, 1987a,b, 1988; Fernandez, 1986). The advantage of using a single dynamic strength test like the 6-ft lift strength test is its ease of use; it takes less than 2 min to conduct. Also, the isoinertial incremental 6-ft lift is a dynamic strength test and is an appropriate input for psychophysical lifting capacity models, since lifting is a dynamic activity. Finally, the isoinertial incremental 6-ft lift is a safe strength test.

Definitions

· The study of the relationship between physical activities and the human perception as to their difficulty

· In the context of ergonomics, it is how we perceive work.

Principles

· Psychophysics tends to show that people work at a place natural to them.

· Approximately the same as a walking pace of 3 mph or

· One liter of oxygen per minute (33% of the VO2 max).

· Given control of at least one work variable (time, frequency, etc.), the worker will adjust that variable in order to perform the task at a “natural” level of output, while not becoming injured.

Psychophysical Scales

· Measurement of how perceived intensities vary with physical or physiological intensities

· Estimation of effort, exertion, and fatigue during physical work.

Benefits:

· Provides valuable information about a subject during any study

· Does not take much time to administer

· Can be used within a battery of tests.

Limitations:

· Subjects cannot be expected to give absolutely valid or reliable ratings.

DISCUSSION

As discussed in the introduction, psychophysical scales have been around a long time. The Borg Scale of Perceived Exertion is one of the most widely used scales. Around the world in health clubs on the walls beside treadmills, stationary bikes, and step machines, one often sees a scale going from 6 to 20. This is called an RPE Scale, which stands for “Rate of Perceived Exertion”. It is a psychophysiological scale, meaning it calls on the mind and body to rate one's perception of effort. Understanding the meaning and use of this chart will benefit the average fitness enthusiast.

The RPE scale measures feelings of effort, strain, discomfort, and/or fatigue experienced during both aerobic and resistance training. One's perception of physical exertion is a subjective assessment that incorporates information from the internal and external environment of the body. The greater the frequencies of these signals, the more intense the perceptions of physical exertion. In addition, response from muscles and joints helps to scale and calibrate central motor outflow commands. The resulting integration of feedforward–feedback pathways provides fine-tuning of the exertional responses.

Perceived exertion reflects the interaction between the mind and body. That is, this psychological parameter has been linked to many physiological events that occur during physical exercise. These physiological events can be divided into respiratory/metabolic (such as ventilation and oxygen uptake) and peripheral (such as cellular metabolism and energy substrate utilization). Previous studies have demonstrated that an increase in ventilation, an increase in oxygen uptake, an increase in metabolic acidosis, or a decrease in muscle carbohydrate stores are associated with more intense perceptions of exertion. The scale is valid in that it generally evidences a linear relation with both heart rate and oxygen uptake during aerobic exercise.

THE BORG RPE SCALE AND THE BORG CR10 SCALE

Borg RPE Scale:

· Most commonly used scale (preferable over CR10 for perceived exertion)

· 15-point scale (between 6 and 20)

· 9 corresponds to “very light” exercise. For a healthy person, it is like walking slowly at his or her own pace for few minutes.

· 13 on the scale is “somewhat hard” exercise, but it still feels OK to continue.

· 17 “very hard” is very strenuous. A healthy person can still go on, but he or she really has to push him- or herself. It feels very heavy, and the person is very tired.

· 19 on the scale is an extremely strenuous exercise level. For most people, this is the most strenuous exercise they have ever experienced.

· Research found that there is a correlation between an athlete's RPE and their heart rate, lactate levels, %VO2 max, and breathing rate.

· A general rule of thumb is to multiply the RPE by 10 to estimate the heart rate. For example, if a person's RPE is 12, then 

, so the heart rate should be approximately 120 beats/min.

Borg CR10 Scale:

· “Category-Ratio” Scale

· Anchored at the number 10, representing extreme intensities

· 9-point scale (between 1 and 10)

· 1 corresponds to “very light” exercise. For a healthy person, it is like walking slowly at his or her own pace for few minutes.

· 3 on the scale is “somewhat hard” exercise, but it still feels OK to continue.

· 5 on the scale is associated with fatigue, but you don't have difficulties.

· 7 “very hard” is very strenuous. A healthy person can still go on, but he or she really has to push him- or herself. It feels very heavy, and the person is very tired.

· 10 on the scale is an extremely strenuous exercise level. For most people, this is the most strenuous exercise they have ever experienced.

· 11 or higher is an “absolute maximum,” which is more than ever experienced.

· Can also be used to rate pain (preferable over RPE).

· Smaller number scale can be limiting.

· Scale does not have a linear relationship with exercise intensity.

BORG SCALES WORKSHEETS

The following worksheets are provided as a framework for using the Borg Scales. The format of the worksheets includes both the instructions to be presented to the subject and the scale itself with descriptions.

Worksheet 1: Borg's RPE Scale

Instructions

While doing physical activity, we want you to rate your perception of exertion, that is, how heavy and strenuous the exercise feels to you, combining all sensations and feelings of physical stress, effort, and fatigue. Do not concern yourself with any one factor such as leg pain or shortness of breath but try to focus on your total feeling of exertion.

Look at the rating scale below while they are engaging in an activity; it ranges from 6 to 20, where 6 means “no exertion at all” and 20 means “maximal exertion.” Choose the number from below that best describes their level of exertion. This will give them a good idea of the intensity level of their activity, and can use this information to speed up or slow down movements to reach their desired range.

Try to appraise their feeling of exertion as honestly as possible, without thinking about what the actual physical load is. Try not to over- or underestimate the rating. Their own feeling of effort and exertion is important, not how it compares to other people. Look at the scales and the expressions and then give a number (Table 8.2).

Table 8.2  Borg Scale Worksheet

6	No exertion at all
7	Extremely light
8
9	Very light (walking slowly at your own pace)
10
11	Light
12
13	Somewhat hard (exercise but feels OK to continue)
14
15	Hard (heavy)
16
17	Very hard (very strenuous, but you are fatigued)
18
19	Extremely hard (extremely strenuous and cannot continue for long)
20	Maximal exertion

Source: Adapted from Borg's Perceived Exertion and Pain Scales.

Worksheet 2: Borg's CR10 Scale

Instructions

10, “Extremely strong” is the main anchor. It is the strongest perception one have ever experienced. It may be possible to experience something stronger; therefore, “Absolute maximum” is further down the scale without a fixed number (•). If one perceive intensity stronger than 10, they may use a higher number (Table 8.3).

Table 8.3  10-Point Borg Scale

0	Nothing at all
0.3
0.5	Extremely weak (just noticeable)
1	Very weak (walking slowly at your own pace)
1.5
2	Weak (light)
2.5
3	Moderate (exercise, but feels OK to continue)
4
5	Strong (heavy)
6
7	Very strong (very strenuous, but you are fatigued)
8
9
10	Extremely strong (as hard as ever experienced)
11
•	Absolute maximum (highest possible)

Source: Adapted from Borg's Perceived Exertion and Pain Scales.

Start with a “verbal expression” and then choose a number. If the perception is “Very weak,” say 1; if “Moderate,” say 3, etc. They can use fractions of points as well. It is important to use values that they perceive, not what they believe they should report. Be honest and try not to over- or underestimate the intensities.

1. Scaling perceived exertion: Rate their perceived exertion, in other words, how heavy or strenuous the physical activity feels to them. This depends mainly on the strain and fatigue in their muscles, feelings of breathlessness or aches in the chest. They must only attend to their subjective feelings and not to the physiological cues or what the physical activity actually is.

2. Scaling pain: Think of your worst experiences of pain. If they use 10 as the strongest exertion they have ever experienced, then think about the three worst pain experiences they have ever had.

10	10 “Extremely strong”: Main point of reference as it is anchored in their previously experienced worst pain
•	The feeling that is somewhat stronger than the worst pain experienced (10). If much stronger, like 1.5 times, then 15.

CASE STUDY – ERGONOMIC ASSESSMENT OF THE FIRING OF THE M198 HOWITZER

Abstract

The United States Marine Corps Artillery Instructional Battery stationed at The Basic School Marine Corps Base Quantico, VA, was experiencing a high rate of injuries and our ergonomics team was asked to perform an analysis of the operation to help determine why these injuries were occurring. We designed and carried out an ergonomics study to determine causes of these injuries. The study was carried out using data collection methods that would collect anthropometric, psychophysical, biomechanical, and human error data. This paper focuses on the anthropometric and psychophysical aspects of the study. The 15-point and 11-point Borg Scales were used as the data collection instruments. At the end of the first day of the study, the Marines were experiencing a high level of fatigue and pain based on their perceptions. Recommendations were made based on the findings from the study.

Highlights

· Members of the Artillery Instructional Battery (AIB) were experiencing many injuries.

· The command requested an ergonomic assessment to determine the causes of the injuries.

· The Borg Scales were used to aid fatigue, exertion, and the ergonomic analysis of the tasks associated with firing of the M198 Howitzer.

· The study showed that the gun crews were experiencing a high level of fatigue followed by pain.

· Recommendations were made to reduce the apparent causes of the fatigue and pain.

Acknowledgments

We wish to thank Cathy Rothwell of Navy Ergonomics with the Naval Facilities Command for her support of this work.

We also wish to thank Anna Smith of The Basic School Safety Office at Marine Corps Base Quantico, VA, for her great help during the data collection phase of the project.

Introduction

The first assignment a United States Marine Corps officer has after obtaining his commission is at The Basic School (TBS) at Camp Barrett, Marine Corps Base Quantico, VA.

TBS further prepares young officers for their military careers by providing them training in a range of topics. The course has 1585 h of training: spending 932.6 h (60%) in the classroom and 652.5 h (40%) in the field. Classroom events include platform instruction, tactical decision games (TDGs), sand table exercises (STEXs), and small group discussions. There are various field events, beginning with fire team and squad level, moving all the way up to platoon-reinforced events. The field events consist of realistic blank-fire training, SESAMS (similar to paintball), and live fire range (Fleet Marine Force, n.d.).

One of the exercises is a Call for Fire from field artillery. This exercise is conducted approximately every 45 days. In this exercise, the new Second Lieutenants (2nd LTs) determine what type of artillery support they need for a scenario and call in the coordinates into a fire support center. The fire support center determines the fire solution and sends this information to the AIB. The AIB then provides the fire support via one of three 155-mm M198 Howitzers. The AIB is a company that consists of 34 very professional, dedicated, and hardworking Marines.

The AIB was experiencing a high number of injuries and our ergonomics team was asked to perform an analysis of the operation to help determine why these injuries were occurring and provide solutions with regard to military-specific constraints.

Description of Activity

The Call for Fire exercise takes place over 3 days. During the first day, the AIB sets up four M198 Howitzers. Three will be active during the exercise and the fourth is considered a “ghost gun” and is kept in reserve. The ammunition is also delivered during day one. Approximately 1100 rounds of 155-mm ammunition, fuses, and sufficient powder are brought to the site. Days two and three are when the actual firing of the guns occurs. Each gun will fire between 350 and 400 rounds of ammunition. The rounds weigh between 95 and 105 lb each depending on whether they contain high explosive or white phosphorus. We did not survey the Marines on day one but much of the setup requires manual materials handling.

The normal gun crew consists of the following members:

· Chief of the gun

· Gunner

· A-gunner

· Recorder

· Powder man

· Ammo team chief

· Two ammo handlers

· Rammer.

Figures 8.1 and 8.2 show aspects of the M198 Howitzer loading process.

Figure 8.1  Marines pick up round in loading tray

Figure 8.2  Marines ram a round into the breach of the M198 Howitzer

The crews of the guns during the shoot consisted of 6–7 members due to Marines on the injured list. The limited human resources made it difficult to rotate the crew as would be done when a full crew complement were available.

The fire process included the following:

1. The fire instructions are radioed to the recorder.

2. The recorder announces the fire order.

3. The powder man adjusts the powder.

4. The type of round to be fired is verified.

5. A round is removed from the ready board and laid into the loading tray.

6. The two loaders pick up the round.

7. The rammer places the ram at the back of the round.

8. The breach is opened.

9. The loaders bring the round up to the breach.

10. The rammer pushes the round in the breach.

1. The loader on the right side of the loading tray releases his grip.

2. The other loader steps back and to the left of the gun.

3. The powder man brings up the powder and hands it to the A-gunner.

4. The A-gunner verifies the amount of powder and places it in the breach.

5. The A-gunner closes the breach and places a primer in the priming hole.

6. The lanyard is attached and then pulled.

7. The gun fires.

8. The A-gunner opens the breach and swabs the breach and breach plug.

Variations occurred in this process based on the health of the crew and the number of crew members available. These variations will be discussed in the course of the article.

Ergonomic Study

The ergonomic study was designed to collect the following data:

1. Anthropometric data

2. Psychophysical measures of exertion, fatigue, and pain using the Borg Scale

3. Qualitative data on activities

4. Biomechanical data

5. Human error data

6. Activity performance data.

Only the anthropometric data and psychophysical aspects of the study will be discussed in this paper due to the great amount of data collected.

A quasi-experimental design was used to conduct the study. As with any active data collection process, participants tend to alter their activities. Therefore, the ergonomics team did their best to not interfere with the activities. Naturalistic observation techniques were used, as well as noninvasive inquiry at times when the Marines were not actively engaged in loading and firing the Howitzers.

The setup was conducted on Monday, August 10, 2009. The AIB setup consisted of four 155-mm M198 Howitzers. The number one gun was a ghost gun or the spare. Guns two through four were to be used on the next 2 days. The AIB also received 1100 rounds of ammunition and corresponding powder and fuses. The setup began at approximately 0600 and finished at approximately 1600. During the afternoon, the ergonomics team collected the anthropometric data and conducted the training of the Marines. Table 8.4 contains the anthropometric data collected.

Table 8.4  Marines Demographic Data

Marine	Stature	Weight	Shoulder to Mid-hand Length	Shoulder Width	Age	Months in Marines	Months at This Assignment	Number of 2-day Shoots
1	73	200	32.0	19.0	23	59	14	24
2	68	195	30.3	17.5	22	56	9	6
3	69	185	28.0	18.5	31	88	36	48
4	73	235	32.0	19.0	25	73	14	26
5	71	200	28.6	18.5	24	68	4	4
6	70	190	29.6	19.0	26	63	12	10
7	72	215	31.0	19.0	26	73	16	25
8	67	168	28.6	17.5	25	90	19	30
9	72	195	28.5	19.5	23	62	10	20
10	67	166	26.5	19.0	24	60	10	10
11	68	180	29.0	20.0	24	62	14	30
12	64	132	25.5	18.0	27	96	4	16
13	73	165	32.3	18.5	23	61	16	32
14	66	168	26.3	19.0	26	67	17	34
15	72	188	29.9	19.0	22	62	15	30
16	67	180	27.8	19.0	26	89	36	48
17	81	245	34.5	21.5	27	67	24	48
18	68	170	29.6	19.0	23	60	12	24
19	69	170	29.3	19.0	25	68	16	25
20	71	202	30.0	19.0	23	63	15	30
21	70	210	28.4	20.0	24	68	18	36
23	71	130	30.0	17.0	25	68	18	30
25	69	170	29.4	18.5	25	61	16	25
28	70	189			25	84	24	24
31	65	193	27.0	19.0	26	84	12	24
Mean	69.8	185.6	29.3	18.9	24.8	70.1	16.4	26.4
Median	70	188	29.3	19	25	67	15	25
Mode	67	170	32	19	25	68	16	30
Std	3.4	26.3	2.1	0.9	1.9	11.5	7.7	11.7
Min	64	130	25.5	17	23	56	4	4
Max	81	245	34.5	21.6	31	96	36	48

On Tuesday, August 11, 2009, the crews arrived at approximately 0600. The Call for Fire exercise began at 0820. The ergonomics team collected data on the activities the Marines had done the day before and whether the Marines ate that morning. The day was going to be hot, so heat stress precautions were going to be in place. A wet bulb globe temperature (WBGT) was positioned near the firing range to monitor the heat index level. The WBGT was only periodically monitored; however, heat index did reach black flag conditions (>90 °F or >32.2 °C) in the afternoon (Weather Information, n.d.).

The ergonomics team observed the entire shoot and collected data as activities permitted. The AIB rested for approximately 1200–1300 for lunch break and during an airstrike from approximately 1330–1415. Data collection ended at 1800.

On Wednesday, August 12, 2009, the shoot began very similar to how it had on Tuesday. The AIB arrived at approximately 0600 and the Call for Fire exercise began at approximately 0730. At approximately 1100, a ceremony was conducted and missions ceased during this time frame. Also, in the afternoon, the 2nd LTs were allowed to help move the rounds that gave the AIB crew adequate rest breaks and data collection ceased at this time. Data collection ended at 1800.

Anthropometric and Demographic Data

Psychophysical Measures of Exertion, Fatigue, and Pain – Borg's Scale

There are a variety of methods for determining exercise intensity levels. Common methods include the target heart rate range (Activity Measurement, n.d.) and the Borg RPE (Borg, 1998). We needed a method of data collection that was noninvasive, and the RPE is a noninvasive technique.

1. The 15-point Borg Scale (6–20) was used to collect indications of exertion.

2. The 11-point Borg Scale was used to collect indications of pain and fatigue.

The following directions were given to the AIB crew prior to the exercise:

At intermittent times during the shoot, the ergonomists will ask you to gauge your feeling of exertion. This feeling should reflect how heavy and strenuous the activity feels, combining all sensations and feelings of physical stress, effort, and fatigue. Do not concern yourself with any one factor such as leg pain or shortness of breath but try to focus on your total feeling of exertion.

Look at the rating scale below while engaging in an activity; it ranges from 6 to 20, where 6 means “no exertion at all” and 20 means “maximal exertion.” Choose the number from below that best describes the level of exertion you feel at this time. This is a good indication of the intensity level of the activity.

Try to appraise the feeling of exertion as honestly as possible, without thinking about what the actual physical load is.

Analogous instructions were given concerning the pain and fatigue data for use with the 11-point scales. The key point to using these scales is the calibration of the participants in the study. Therefore, prior to the data collection efforts, every Marine who participated in the study was briefed as to what the scales and the level of the scales meant.

Exertion, fatigue, and pain data were collected at random intervals. However, data was not collected from every Marine at every interval. The reason was because of the activities the Marines were involved in at the data collection times.

Fire missions during the data collection varied from one round to seven, with most being 3, 4, or 6 rounds.

Results

As discussed above, indicators of exertion, fatigue, and pain were collected at random intervals and at times that impacted the Marines the least. However, they were documented as close to a 60-min interval as possible. Table 8.5 shows the means of these values.

Table 8.5  Means of Exertion, Fatigue, and Pain Values for Day 1

Value	colspan="9">Time of Day
	0800	0900	1000	1100	1200	1300	1530	1700	1800
Exertion	6.14	6.14	8.4	14	9.4	11.88	13.8	14.25	15.53
Fatigue	3.14	3.2	2.0	6.0	3.7	5.85	6.9	7.34	8.37
Pain	1.0	0.71	1.4	1.0	2.83	2.88	3.95	5.42	6.5

Figure 8.3 shows the change in the mean value for exertion, Figure 8.4 shows the change in the mean value for fatigue, and Figure 8.5 shows the change in the mean value of pain over the course of day 1. The indicators trend with time and activity, increasing as the day goes on, leveling off during rest and then increases again with resumed activity. Figure 8.6 compares pain and fatigue as they trend.

Figure 8.3  Change in mean exertion levels – day 1

Figure 8.4  Changes in mean fatigue levels – day 1

Figure 8.5  Changes in mean pain levels – day 1

Figure 8.6  Comparisons of fatigue and pain levels

It is apparent in these graphs that as the day progresses, the perceptions of exertion, fatigue, and pain increase. However, the level for pain stayed relatively low for a considerable amount of the day, but at approximately 1300 h it increased rapidly. Fatigue, on the other hand, increased in the morning, but after a break, around noon due to a simulated air support exercise in which the AIB did not participate, the fatigue level dropped. It then increased rapidly after the firing began again. It is also apparent that pain lags slightly behind fatigue as the day progresses.

The question was asked whether these increases were statistically significant. In other words, the hypothesis is that there is no statistical difference between the perceptions of exertion, fatigue, and pain as the day progressed. The t-test for unequal variances was used to test this.  Tables 8.6 – 8.8  show the detailed results of some of these tests. Further results are summarized in  Tables 8.6 – 8.8 . However, it is important to note that in this study statistical significance may or may not provide more information than is displayed in the proceeding graphs. This is because data were not gathered at uniform times from the Marines, and it appeared to us that the Marines got better at reporting values as time went along. Of course, the reason for the lack of statistical significance is due to the variability of the data.

Table 8.6  Results of t-Test for Exertion at 0900 and 1300

Factor	0900	1300
Mean	6.142857	11.88889
Variance	10.47619	12.86111
Observations	7	9
df	14
t-Statistic	3.35938
P(T ≤ t) one-tail	0.002338
t-Critical one-tail	1.76131

Table 8.7  Results of t-Test for Fatigue at 0900 and 1300

Factor	0900	1300
Mean	3.222222	5.85
Variance	3.944444	3.669444
Observations	9	10
df	17
t-Statistic	2.92841
P(T ≤ t) one-tail	0.00469
t-Critical one-tail	1.739607

Table 8.8  Results of t-Test for Pain at 1300 and 1500

Factor	1300	1500
Mean	2.875	3.95
Variance	4.125	2.136111
Observations	8	10
df	12
t-Statistic	1.25885
P(T ≤ t) one-tail	0.116011
t-Critical one-tail	1.782288

Tables 8.9 – 8.11  show statistical comparisons of the data at 0900 on day 1 and 0900 on day 2. Only pain is statistically significantly different from day 1 to day 2. Exertion and fatigue levels are not statistically significantly different. This is an indication that the Marines recovered somewhat but not fully. Lasting pain can be a precursor to injury development (see  Tables 8.12 – 8.14 ).

Table 8.9  Statistical Significance of Pair-Wise Comparison of Exertion

colspan="5">Comparisons of Exertion Indicators at Time Intervals
Factor	0900–1300	1300–1530	1530–1700	1700–1800
Mean	6.1 versus 11.9	11.9 versus 13.8	13.8 versus 14.3	14.3 versus 15.5
t-Statistic	−3.35938	1.35813	0.31641	0.67007
t-Critical one-tail	1.7613	1.76131	1.734064	1.717144
Statistical significance	Yes	No	No	No

Table 8.10  Statistical Significance of Pair-Wise Comparison of Fatigue

colspan="5">Comparisons of Fatigue Indicators at Time Intervals
Factor	0900–1300	1300–1700	1500–1700	1700–1800
Mean	3.2 versus 5.9	5.9 versus 6.9	6.9 versus 7.3	7.3 versus 8.6
t-Statistic	2.92841	1.61751	0.7124	1.86881
t-Critical one-tail	1.739607	1.782288	1.745884	1.729133
Statistical significance	Yes	No	No	Yes

Table 8.11  Statistical Significance of Pair-Wise Comparison of Pain

colspan="5">Comparisons of Pain Indicators at Time Intervals
Factor	0900–1300	1300–1500	1500–1700	1700–1800
Mean	0.7 versus 2.9	2.9 versus 4.0	4.0 versus 5.4	5.4 versus 6.5
t-Statistic	2.51158	1.25885	2.0668	1.31278
t-Critical one-tail	1.782288	1.782288	1.720743	1.705618
Statistical significance	Yes	No	Yes	No

Table 8.12  Results of t-Test for Exertion Day 1 to Day 2 at 0900

Factors	Exertion 0900 Day 2	Exertion 0900 Day 1
Mean	8.25	6.142857
Variance	0.25	10.47619
Observations	4	7
df	6
t-Statistic	1.687552
t-Critical one-tail	1.94318

Table 8.13  Results of t-Test for Fatigue Day 1 to Day 2 at 0900

Factors	Fatigue 0900 Day 2	Fatigue 0900 Day1
Mean	4.083333	3.222222
Variance	2.041667	3.944444
Observations	6	9
df	13
t-Statistic	0.975924
t-Critical one-tail	1.770933

Table 8.14  Results of t-Test for Pain at 0900 Day 1 to Day 2

Factors	Pain 0900 Day 2	Pain 0900 Day 1
Mean	2.25	0.714286
Variance	0.25	1.571429
Observations	4	7
df	8
t-Statistic	2.866667
t-Critical one-tail	1.859548

Table 8.15  shows statistical comparisons of the data at 1200 for pain for day 1 and day 2. Exertion and fatigue were not tested because of lack of data. There was no statistically significant difference between the 2 days at 1200.

Table 8.15  Results of t-Test for Pain at 1200 Day 1 to Day 2

Factors	Pain Day 2 1200	Pain Day 1 1200
Mean	2.8	2.833333
Variance	2.26	6.151515
Observations	6	12
df	15
t-Statistic	−0.03535
t-Critical one-tail	1.75305

The data analysis shows that the Marines' perceptions of exertion, fatigue, and pain increase statistically significantly over time. The Marines are performing the same level of exertion on the second day at 0900 as the first day at 0900 and have the same level of fatigue. However, the perception of pain is increased. Once the Marines have additional help in the afternoon of the second day by the 2nd LTs, their perceptions of fatigue and pain levels drop significantly. In fact, data collection in the afternoon of day 2 ceased because the Marines stated they were no longer fatigued.

Regression analyses were performed between anthropometric data and the psychophysical indicators of pain and fatigue.  Table 8.16  shows the results of the analysis for the relationship between stature and pain. The result of this analysis shows there is little to no relationship between these two variables because the R2 value is only 0.23.  Table 8.14  shows the results for the relationship between stature and fatigue and  Table 8.17  shows the results for the relationship between weight and fatigue. These tables and  Table 8.18 , show there is little to no relationship between anthropometric variables and perceptions of pain. Similar comparisons were conducted between age and fatigue and pain and these comparisons also show no statistical relationship (see  Table 8.19 ).

Table 8.16  Regression Analysis of Stature and Pain at 1800 Day 1

colspan="2">Regression Statistics
Multiple R	0.479674
R2	0.230087
Adjusted R2	0.160095
Standard error	3.561562
Observations	13

Table 8.17  Regression Analysis of Stature and Fatigue at 1800 Day 1

colspan="2">Regression Statistics
Multiple R	0.189022186
R2	0.035729387
Adjusted R2	−0.044626498
Standard error	4.204556406
Observations	14

Table 8.18  Analysis of Weight and Fatigue at 1800 Day 1

colspan="2">Regression Statistics
Multiple R	0.118799
R2	0.014113
Adjusted R2	−0.06804
Standard error	30.96039
Observations	14

Table 8.19  Analysis of Weight and Pain at 1800 Day 1

colspan="2">Regression Statistics
Multiple R	0.258599
R2	0.066874
Adjusted R2	−0.01796
Standard error	26.96009
Observations	13

KEY POINTS

The findings from psychophysical aspects of the study were as follows:

1. The Marines' perceptions of exertion, fatigue, and pain increase statistically significantly over the course of the day. Once a break is provided for the Marines, their perceptions of exertion, fatigue, and pain decrease.

1. There is no relationship between anthropometric measurements or demographics and exertion, fatigue, and pain. This indicates that the increases in these factors are due to the task and not due to anthropometrics or demographics of the Marines.

2. Upon being given additional help by the 2nd LTs on day 2 the Marines' perceptions of exertion, fatigue, and pain reduced to the point the Marines felt they were no longer overexerted, fatigued or in pain.

The recommendations based on these findings were as follows:

1. More Marines need to be added to the AIB Company to support the shoots. The optimal number would be 9–10.

2. The 2nd LTs should be allowed to move the rounds, thus significantly reducing the number of lifts the Marines perform.

3. Providing additional aid, either with more Marines or allowing the 2nd LTs to help, reduces the exposure of loading the gun to within acceptable levels according to the MIL-STD 1472F.

The US Marine Corps has implemented several changes to this process since the study was conducted. Most notably, they increased the number of Marines in the AIB Company.

REVIEW QUESTIONS

1. What are the inherent differences between the 15-point and the 10-point Borg Perceived Exertion Scales?

2. What is the advantage of using the Borg Scale over collecting physiological data?

3. Is the Borg Scale appropriate for assessing all tasks? Why or why not?

4. Develop a study to assess some activity, such as a lifting task. What are the advantages and disadvantages over using the NIOSH lifting equation?

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