Analysis of applied forces and electromyography of back and shoulders muscles 

when performing a simulated hand scaling task 

William Porter*, Sean Gallagher, Janet Torma-Krajewski 

Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, 626 Cochrans Mill Road, P.O. Box 18070, Pittsburgh, PA 15236

* Corresponding author. Tel.: þ1 (412)386 5222; fax: þ1 (412)386 6710.

E-mail address: wlporter@cdc.gov (W. Porter).

abstract

Hand scaling is a physically demanding task responsible for numerous overexertion injuries in underground mining. Scaling requires the miner to use a long pry bar to remove loose rock, reducing the 

likelihood of rock fall injuries. The experiments described in this article simulated ‘‘rib’’ scaling (scaling 

a mine wall) from an elevated bucket to examine force generation and electromyographic responses 

using two types of scaling bars (steel and fiberglass-reinforced aluminum) at five target heights ranging 

from floor level to 176 cm. Ten male and six female subjects were tested in separate experiments. Peak 

and average force applied at the scaling bar tip and normalized electromyography (EMG) of the left and 

right pairs of the deltoid and erectores spinae muscles were obtained. Work height significantly affected 

peak prying force during scaling activities with highest force capacity at the lower levels. Bar type did not 

affect force generation. However, use of the lighter fiberglass bar required significantly more muscle 

activity to achieve the same force. Results of these studies suggest that miners scale points on the rock 

face that are below their knees, and reposition the bucket as often as necessary to do so. 

1. Introduction

The roof and ribs (i.e., walls) of underground mines are regularly 

examined and scaled with a long pry bar to remove loose surface 

rock. The purpose of this activity is to reduce the likelihood of rock 

fall injuries and is a safety activity mandated by the U.S. Mine Safety 

and Health Administration (MSHA). Hand scaling is a physically 

demanding task, and is associated with numerous overexertion 

injuries. Two-thirds of scaling-related overexertion injuries involve 

the back and shoulders with the major injury being a pulled back 

muscle (MSHA, 2000–2004). The average number of lost days per 

scaling overexertion injury was 65 days compared to 28 days lost 

on average for scaling-related injuries as a whole. 

In many high-seam mines (such as underground limestone or 

salt mines), scaling of the mine ribs (i.e., mine wall) requires miners 

to work from an elevated bucket, positioned a few feet from the 

rock face. The distance between the bucket and the rib varies 

depending on how close the bucket can safely be positioned to the 

rib. Occasionally two miners may be scaling from the same 

the bucket. The scaling process starts with a visual inspection of the 

rock face to locate cracks or other signs that a rock must be 

removed. The miner then uses a scaling bar to probe any observed 

cracks for loose rock by jabbing the tip of the scaling bar into the 

crack to determine whether the tip can obtain enough purchase to 

remove a piece of loose rock. Removal is achieved by applying 

a downward shear force often combined with a prying motion to 

pull the loose rock away. Field observations of this task showed that 

once the bucket has been positioned, the miner(s) tend to start 

scaling at shoulder level and work downward, and that the bucket 

is usually not moved until the miners have scaled everything they 

can reach from their current position. 

Previous research on the physical demands of scaling bar use is 

scant. Marras and Lavender (1991) examined overhead roof scaling 

using different weights and types of scaling bars. Their study based 

recommendations on predicted spine compression forces and 

striking force at the tip of the scaling bar. The authors found predicted spine forces lower for the lighter bar which gave slightly 

lower average striking force, but this difference was not statistically 

significant. It was also found that a counterbalanced scaling bar 

(with more bar weight closer to the operator) significantly reduced 

low back loading. However, this research looked only at overhead 

scaling bar use and not wall-scaling activities, for which physical 

demands would differ considerably. Therefore the goal of the 

present investigation was to evaluate the force generation capabilities and electromyographic responses to simulated rib scaling 

exertions in a laboratory setting. Specifically, the focus of these 

studies was the downward force application since the maximum 

effort occurs during this subtask. Improved knowledge of the 
physical demands and worker capabilities associated with this 

scaling task should allow better recommendations for appropriate 

work height, bar type and bucket position to reduce overexertion 

injury risk. 

2. Methods

2.1. Subjects

A total of sixteen subjects (10 males and 6 females) were tested. 

The male subjects had a mean age of 46.1 years (SD 1⁄4 6.4) and the 

female subjects had a mean age of 37.3 years (SD 1⁄4 11.3). Two of the 

male subjects had previous experience with hand scaling in 

a mining environment; none of the females had such experience. 

Subjects in both studies were volunteers and operated under terms 

of informed consent. Male subjects had a mean height of 180.3 cm 

(SD 1⁄4 3.8 cm) and a mean weight of 90.5 kg (SD 1⁄4 10.28 kg). The 

female subjects had a mean height of 163.8 cm (SD 1⁄4 15.22 cm) and 

a mean weight of 68.6 kg (SD 1⁄4 10.58 kg). All subjects except for 

one female were right hand dominant. However, this subject also 

indicated that she played sports right handed and, for consistency, 

was asked to perform the task in the same manner as the other 

subjects. Prospective subjects were excluded if they had not 

completely recovered from prior musculoskeletal injury, or if any 

other medical condition contraindicated their participation. 

2.2. Experimental design

Testing of the male and female subjects were considered separate studies, but both employed the same experimental paradigm. 

Two independent variables, the height of the target on which the 

force was generated (five levels) and the scaling bar type (two 

levels), were investigated. Dependent variables consisted of peak 

and mean downward force (in Newtons) generated by the subject 

against a uni-axial dynamometer at five specified target heights 

(THs), and peak and mean normalized surface electromyographic 

(EMG) activities from four muscles as detailed below (Keppel, 1991; 

Kirk, 1995). As discussed previously, the predominant injuries 

observed in scaling bar tasks were injuries to the back and shoulder. 

For this reason the authors examined the activity of muscles that 

were most related to injury mechanisms of those joints. The 

muscles selected were the erectores spinae (the primary loader of 

the low back) and the medial head of the deltoid (an important 

anterior stabilizer of the shoulder joint). 

A split-plot experimental design was used where subjects were 

treated as whole plots (with target height treated as main plot 

factor), and scaling bar type constituted the sub-plot factor. This 

design required two separate randomizations within each subject. 

First, randomization of the target heights was performed, and 

within each level of this variable a restricted randomization of 

scaling bar type was performed. Three replications of each 

combination of target height and bar type were executed, for a total 

of 30 trials per subject (Keppel, 1991; Kirk, 1995). The data from the 

replications were combined for the analysis. 

2.3. Procedure

EMG electrodes were placed on the skin’s surface above the 

medial divisions of the left deltoid (LD) and right deltoid (RD), along 

with the left erectores spinae (LES) and right erectores spinae (RES) 

muscle groups (L3 lumbar level). The signal was collected at 

1000 Hz and amplified using a low noise instrumentation amplifier 

with a common-mode rejection ratio of 110 dB. All EMG signals 

were processed using a high-pass filter to remove potential motion 

artifacts in the form of frequencies below 20 Hz and a low-pass 

filter to remove unwanted frequencies above 450 Hz. The EMG 

signal for each muscle was normalized to signals obtained during 

maximal voluntary contractions (MVC). For the back muscles, the 

MVC consisted of an isometric trunk extension against resistance 

from a flexed posture. For the deltoids, the MVC consisted of 

shoulder abduction against resistance. 

A force gauge was mounted on a wall at one of five heights, as 

illustrated in Fig. 1. The subjects were standing at a horizontal 

distance of 183 cm from the force gauge. The minimum horizontal 

distance was determined by the distance that must be maintained 

to keep the miners safe. This distance was chosen based on field 

observations of the task made by NIOSH researchers and represented a worst case scenario. The five vertical THs of the force gauge 

were 0, 56, 107, 144, and 176 cm. The upper four heights roughly 

correspond to the average knee, waist, shoulder and stature for 

a 50th percentile male and 95th percentile female. Females were 

tested at the same heights since females may be required to scale at 

similar heights to males if working in tandem in an elevated bucket. 

Since the female subjects participating in this study were about 

50th percentile in height, the authors acknowledge that the female 

subjects were at a biomechanical disadvantage at the higher THs as 

compared to the male subjects, and that this disadvantage could 

affect the results of this study. 

Fig. 1. Experimental setup. Gray figure represents approximate subject posture at the 

lowest TH; outlined figure represents approximate subject posture at the highest TH. 

Forces were not measured at the hands, but were predominantly in a downward 

direction. 

Two types of scaling bar (SB) were tested: one made of steel, the 

other consisted of a hollow aluminum pipe reinforced with fiberglass. Marras and Lavender (1991) identified the common length of 

the bars to be 245 cm long, so this bar length was used in this study. 

The steel bar weighed 6.4 kg with a diameter of 2.5 cm and 

a deflection upon load of 15 mm, while the fiberglass bar weighed 

4.0 kg with a diameter of 4.0 cm and a deflection upon load of 

6 mm. The deflection upon load of the scaling bars was found by 

supporting the bar at both ends and applying a 23 kg load to the 

middle of the bar and measuring the deflection of the bar from 

resting position. Both bars ended in a straight chisel tip. 

To ensure correct placement of the bar, the tip was placed on the 

dynamometer by researchers before each test. Subjects’ hand 

placements were not restricted and they were allowed to hold the 

bar as they typically would for a similar task. The subjects were not 

allowed to move their hands during the individual trials. During 

testing, little variation in subject hand placement was observed. 

Typically, the subjects would grasp the bar with their dominant 

(right) hand near the end of the scaling bar and the other (left) hand 

around the mid-point of the bar. Subjects were then asked to apply 
a downward maximum voluntary isometric muscular force in 

accordance with standard isometric strength testing procedures, 

with 2 min of recovery time given after each trial (Caldwell et al.,

1974). The subjects were asked to apply a force for a total of five 

seconds. The force applied over the last three seconds of the trial 

was averaged to find the mean force per trial. The peak force was 

determined as the maximum force over the same three seconds. 

EMG data were collected and analyzed for the matching three 

second period of time. Despite the difference in target heights, the 

subjects’ trunk postures were not observed to vary substantially 

during the performance of the scaling tasks tested. 

2.4. Data treatment

Due to the differences in shoulder strength among males and 

females, it was decided to analyze male subjects and female 

subjects separately (Chaffin et al., 1999). A split-plot analysis of 

variance (a 1⁄4 0.05) was used to determine the effect of the independent variables on the peak and mean downward force generated and peak and mean normalized EMG data. Orthogonal 

polynomials were used for a posteriori tests for trends in force as 

detailed in the results section. The Dunn-Sˇida ́k procedure was used 

for the a posteriori tests to maintain an experiment-wise error rate 

of a 1⁄4 0.05 (Kirk 1995). 

3. Results

3.1. Experiment 1: male subjects

3.1.1. Force generation

Inspection of both peak and mean force data for male subjects 

(Fig. 2) provided strong evidence of U-shaped (quadratic) trends as 

a function of target height, with higher forces observed at target 

heights of 0, 56 and 176 cm, and lower values at the intermediate 

heights (107 and 144 cm above floor level). Accordingly, a posteriori

trend analysis procedures were used to test for the significance of 

the suspected trends. The Dunn-Sˇida ́k procedure was employed to 

examine whether significant quadratic, cubic, or quartic trends 

existed as a function of TH (Kirk 1995). The critical tDS for 4 

orthogonal polynomial contrasts with a 1⁄4 0.05 and 60 error df was 

2.653. The obtained tDS statistic for a quadratic trend for mean 

force was 2.740 (p < 0.05), and for peak force the obtained statistic 

was 3.271 (p < 0.01), both indicative of significant quadratic trends. 

Cubic and quartic components were not significant (p > 0.05). On 

average (across all male subjects and target heights), peak and 

mean forces generated using the two bars were all within a range of 

1 N. 

3.1.2. Electromyography

The type of bar used during the prying task was found to 

significantly affect muscle activity in the male subjects, but the 

height at which the task was done was not significant (p > 0.05). 

For this reason, muscle activation data were aggregated over the 

heights and analyzed with respect to bar type. Separate analyses 

were performed on the mean and peak normalized EMG data. 

The effect of bar type on mean muscle activity is shown in Fig. 3. 

Subjects demonstrated 10% greater mean muscle activity in the left 

deltoid (F1,245 1⁄4 9.41, p < 0.01) and the right erector spinae muscle 

(F1,245 1⁄414.86, p < 0.0001) with the fiberglass bar requiring 

increased activity compared to the steel bar. Fig. 4 illustrates 

a significant interaction between bar type and work height for 

mean muscle activity of the right deltoid (F4,245 1⁄4 2.45, p < 0.05). 

The right deltoid was significantly (p < 0.05) less activated at THs of 

56 and 176 cm when using the steel bar (TH 176 cm contrast 6.15; 

F1,245 1⁄4 7.26, p < 0.01; TH 56 cm contrast 7.05; F1,245 1⁄4 5.89, 

p < 0.05). This interaction may be due to postural changes at these 

two levels or differences in bar properties at these levels. Peak 

muscle activity data, like mean data, demonstrated subjects experienced significantly greater muscle activity for both left 

(F1,245 1⁄4 7.21, p < 0.01) and right deltoids (F1,245 1⁄412.06, p < 0.001) 

when using the fiberglass bar rather than the steel bar. 

70 

75 

80 

85 

90 

95 

100 

105 

110 

0 56 107 144 176 

Target Height (cm) 

Force (N) 

Peak 

Mean 

Fig. 2. Downward force generated as a function of work height for male subjects 

(n 1⁄4 10) (bars represent standard error of the mean). 

0 

10 

20 

30 

40 

50 

60 

70 

Left Deltoid Right Deltoid Left ES Right ES 

Normalized EMG (% MVC) 

Fiberglass 

Steel 

* 

** 

* 

Muscle Group 

Fig. 3. Mean normalized EMG data as a function of bar type for male subjects (n 1⁄4 10) 

(bars represent standard error of the mean) (* significant difference at p < 0.01; 

** significant difference at p < 0.001). 

3.2. Experiment 2: female subjects

3.2.1. Force generation

Female subjects were affected by a significant interaction 

between TH and SB for both peak (F4,145 1⁄4 3.35, p < 0.05) and 

average (F4,145 1⁄4 4.27, p < 0.01) force. Fig. 5 illustrates the interaction for peak force. The peak force generated using the fiberglass 

scaling bar showed a tendency towards the quadratic trend 

exhibited by males. However, force generation varied considerably 

with the steel bar for female subjects. Using the steel bar at floor 

level resulted in the greatest force production overall for female 

subjects. Peak forces at the 56 and 107 cm THs were nearly identical 

for both bars. However, at the upper two THs, the steel bar and 

fiberglass bar reversed in terms of force production, with the steel 

bar having the advantage at the 144 cm TH, and the fiberglass bar 

superior at the 176 cm TH. Mean forces for the females followed the 

same trend as the peak forces but were approximately 5 N lower. 
Forces generated by females were approximately 65% of the force 

generated by males. This percentage was consistent for both peak 

and mean force measures. 

15 

20 

25 

30 

35 

40 

Fiberglass 

Steel 

Normalized Mean EMG (% MVC)

0 56 107 144 176 

Target Height (cm) 

Fig. 4. Interaction effect of the average right deltoid normalized EMG for male subjects 

(n 1⁄4 10) (bars represent standard error of the mean). 

3.2.2. Electromyography

The right deltoid was the only muscle to be significantly affected 

by any of the independent variables for female subjects. The peak 

and mean activities were affected similarly for all THs and SB. Peak 

activity of this muscle was significantly affected by TH (F4,20 1⁄4 4.03, 

p < 0.05). This effect was characterized by a significant increase in 

activity at the 107 and 144 cm THs compared to other THs (Fig. 6). 

Average activity of this muscle was affected by an interaction of TH 

and SB (F4,145 1⁄4 4.53, p < 0.01). The activity associated with the use 

of both scaling bars increased at the 107 and 144 cm THs; however, 

the interaction appears to have been driven by higher average 

deltoid activity at the lower heights for the fiberglass bar than for 

the steel bar. 

Comparison of EMG activity between males and females indicated two primary differences. Males tended to exhibit increased 

higher normalized mean activity in the RES compared to females 

(41% versus 21%), while females exhibited increased mean activity 

in the RD (44% versus 26% for men). These differences in muscle 

activation were consistent across THs and SBs. Activation of other 

muscles was found to be similar (within 5%) for both genders. 

4. Discussion

The objective of this study was to investigate the force generation capabilities and electromyographic responses to a simulated 

hand scaling subtask. Results from the study with the male subjects 

demonstrated that force generation capability was a function of TH 

and muscle activity was primarily a function of bar type. Specifically, TH was found to significantly affect the maximum amount of 

force males generated during this simulated scaling task. This study 

indicated reduced capacity in downward force production when 

the target height was located around the torso region, with higher 

force generation when the target was at higher or (particularly) 

lower levels. The higher forces at lower heights may be attributed 

to application of the weight of the body (leaning into the bar) to 

increase force generated, while higher forces at the 176 cm TH may 

be attributed to ‘‘hanging’’ on the bar with the forward arm to 

increase the amount of force exerted. Around the torso region (with 

a fairly ‘‘level’’ orientation of the scaling bar), subjects could not 

effectively use their body weight to generate additional force with 

the bar, resulting in reduced capacity. As noted in the results 

section, increased muscle activity of RD was increased for THs in 

this region for males, yet was unable to result in higher forces 

generated at the scaling bar tip. Thus, it appears that target heights 

around the waist to shoulder region have a dual penalty with 

respect to rib scaling: increased required muscle activity (evident in 

both genders), yet decreased force output at the scaling bar tip 

(particularly evident in males). 

45 

50 

55 

60 

65 

70 

75 

Peak Force (N) 

Steel 

Fiberglass 

0 56 107 144 176 

Target Height (cm) 

Fig. 5. Peak downward force generated by female subjects by THs and SB (n 1⁄4 6) (bars 

represent standard error of the mean). 

85 

0 56 107 144 176 

Normalized Peak EMG (% MVC) 80 

75 

70 

65 

60 

55 

50 

Target Height (cm) 

Fig. 6. Peak right deltoid activity for female subjects by height (n 1⁄4 6) (bars represent 

standard error of the mean). 

Force generation by females was a product of both SB type and 

TH, which though significant, was not easy to interpret. The 

greatest force capability demonstrated by females was consistently 

the steel bar at floor level, with all other conditions resulting in 

forces within a fairly narrow range and no clearly discernable trend. 

Differences in force generating capabilities between genders in this 

scaling task coincides with data from previous studies indicating an 

overall strength deficit for females compared to males (Astrand and 

Rodahl, 1977). In general, the muscle strength of an adult female is 

lower than that of males for all muscle groups, with the muscle 

strength of females approximately two-thirds that of males 

(Stobbe, 1982; Roebuck et al., 1975), which is almost precisely the 

difference in force generation observed in the present study. 

Scaling may be particularly demanding for females due to high 

requirements on the shoulder muscles, where a greater difference 

in strength between men and women typically exists (Kuhlman 

et al., 1992; Mayer et al., 1994; Amell, 2004). The fact that women 

will be working at a higher percentage of shoulder strength 
capacity may help explain higher muscle activity observed for the 

right deltoid, which was required to hold up the near end of the bar 

and keep it stabilized while exerting force. The force data from the 

female subjects is difficult to interpret due to the presence of 

a significant interaction. The main finding was that their force 

responses were influenced by both TH and SB and were a function 

of the specific combination of these factors. 

When one considers the typical procedure for scaling outlined 

in the Introduction (where miners typically start scaling at shoulder 

height and work their way down), it would appear that the current 

procedure puts the miner at a significant disadvantage at the start 

of the scaling operation until the miner can get to locations that are 

at or below knee height. Force generating capacity appeared related 

to the ability to use mechanical advantages such as body weight. 

This may be particularly important for females, who exhibit an 

overall strength disadvantage. The highest average peak force of 

approximately 70 N for females was at the 0 cm TH. This value was 

just slightly higher than the force of gravity on the steel scaling bar 

used in this study. 

The results of these studies lead to the conclusion that miners 

should scale points on the rock face that are at or below their knees 

and reposition the bucket as necessary to accommodate that work 

height region. While higher force capacity was observed at a TH of 

176 cm, the act of scaling at that level requires a miner to manipulate 

the bar substantially more than at lower THs, which could introduce 

additional joint forces and awkward postures. It must be recognized 

that two miners may be in the same bucket so coordination of the 

bucket movement is a critical aspect of this recommendation. 

The type of bar used, for the male subjects, was not found to 

affect the force generated at any heights tested. However, increased 

muscle activity was required to generate the same amount of force 

with the lighter fiberglass bar as opposed to the heavier steel bar for 

the male subjects. A heavier bar may necessitate more muscle 

activity to hold, lift, and control the bar if the entire task is 

considered. For the subtask studied, results from the male subjects 

suggest that if a miner needs to utilize a tool to exert a force, 

a lighter tool may actually require increased muscle activity to 

reach the same force level generated by a heavier tool. Thus, in the 

case of the subtask under study, the heavier tool may actually 

confer a biomechanical benefit thereby reducing the stresses on the 

body. In addition, the greater deflection of the steel bar may have 

assisted in transferring a greater compressive force to the dynamometer. Proper evaluation of the trade-offs associated with tool 

weight will require additional research. Indeed, it may be necessary 

to use both types of bars and even several different lengths of bar to 

reduce the stress placed on the body given the variety of circumstances that may be encountered while hand scaling. More research 

on scaling tasks and the effects of flexibility, length, size, diameter, 

and weight of various bar types must be completed to offer 

comprehensive recommendations. 

Previous research on scaling bars, as discussed in the Introduction, found that predicted spine forces were lower for the 

lighter bar and gave slightly lower average striking force. The 

results of the current study indicated that it was more difficult to 

get the same downward force when using the lighter bar. Subjects 

had to work harder as indicated by the increased muscle activity to 

accomplish the same task when using the lighter bar. The 

discrepancies in the two findings are probably due to the difference 

in the subtasks examined. 

4.1. Limitations

Certain limitations need to be considered when evaluating these 

data. While the experiment helps define the capabilities of miners to 

generate forces using a scaling bar, certain other aspects of the task 

(such as jabbing of the rock wall) were not able to be accurately 

replicated with the current experimental setup. Potential damage to 

the dynamometer from such activities was a concern to the investigators. Further, the subtask studied in this experiment is not representative of the overall demands of scaling since scaling requires 

multiple subtasks varying in posture, actions, and force. While the 

heavier bar seemed to confer some advantages in the current 

experiment in terms of reducing muscular demands for the experimental task, clearly this advantage may be outweighed in other 

situations such as carrying or lifting the bar for overhead scaling. 

The choice of bars used in this study may also be a limiting factor 

in the generalization of these results. The bars that were identified 

as most common had not only weight differences but also differences in diameter and deflection upon load. Each of these variables 

would have an effect on strength observed. For this reason, the 

results can not be easily distinguished between bars characteristics; instead only the overall bar effect can be discussed. Force 

generating capacity of a scaling bar may also be a function of the bar 

length and horizontal distance from the subject to the target. These 

variables were not examined in this study for simplicity of the 

experimental design. 

Finally, it was decided to test females at the same THs as males 

for comparative purposes; however, these heights probably 

disadvantaged females, particularly at the highest TH. At this TH the 

female subjects were working above their heads; this would mean 

that the shoulder and mid back muscles would be more active. 

Since these muscles were not monitored in this study, the authors 

could not make definitive conclusions on how females responded 

to scaling at this level. The trends identified for the males were not 

seen for the females; this is possibly due to the varied regional 

strength differences of males and females (Chaffin et al., 1999). 

Additional research will be necessary to develop comprehensive 

work practice recommendations that address (in a more holistic 

way) the goal of reducing the injury risk to miners when performing hand scaling activities. 

5. Conclusion

Results of this study support the following conclusions: 

1) The height at which the scaling bar tip is positioned has 

a significant impact on peak and mean force generation capability for male subjects and follows a U-shaped curve with 

highest values for targets at or below 56 cm (knee) height and 

lowest values in the 107–144 cm (waist to shoulder) region. 

2) Peak and mean force generation by females was affected both 

by the height of the scaling target and the bar used. Greatest 

forces were generated using the steel bar at a target height of 

0 cm (floor level) for the females, for both peak and mean force 

data. The female subjects exhibited a similar, but not significant, quadratic trend demonstrated by males when using the 

fiberglass but not the steel scaling bar. 

3) The type of scaling bar (steel or fiberglass) did not affect forces 

applied for the males; however, these subjects showed 

increased EMG activity for the right erectores spinae and left 

deltoid when using the lighter fiberglass bar. For the female 

subjects, no specific scaling bar effect independent of target 

height was identified. 

4) Female subjects were able to generate approximately 65% of 

the force of males at the scaling bar tip. Analysis of muscle 

recruitment indicated higher activity of the right erectores 

spinae for males as compared to females and increased activity 

of the right deltoid muscle in females as compared to males. 

5) Results of this study, for both males and females, suggest that 

repositioning the bucket to allow for scaling of rock at or below 
56 cm (knee level) would be advisable due to the decreased 

force generation capacity when scaling at higher target heights. 

If two miners are in the bucket, position the bucket according 

to the height of the shorter miner or have the taller miner scale 

at higher locations particularly when scaling near the roof. 

Acknowledgments

The authors would like to acknowledge the contributions of the 

following individuals in the conduct of this study: Lisa Steiner, 

Carrie Reinholtz, Mary Ellen Nelson, Al Cook, George Fischer, Bill 

Rossi, David Beshero, and Leigh McClure. 

Disclaimer

The findings and conclusions in this report are those of the 

authors and do not necessarily represent the views of the National 

Institute for Occupational Safety and Health. 

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