Development and initial assessment of objective fatigue measures for apple harvest work
Introduction
Migrant and seasonal farmworkers provide much of the manual labor used in agriculture for planting, pruning and harvesting of fruits and vegetables in the US. One common result of these activities is musculoskeletal strain due to stooping (ground crops), reaching (orchard fruit), and carrying of heavy loads. There is some research evidence to suggest that extreme powerlessness among this largely foreign-born, uneducated and sometimes undocumented workforce contributes to injury frequency (Salazar et al., 2005).
A number of published studies place musculoskeletal strains among the most frequent injuries for migrant and seasonal farmworkers (Northeast Center for Agricultural and Occupational Health, 2003, unpublished; Villarejo and Baron, 1999; Osorio et al., 1998; Husting et al., 1997; Ciesielski et al., 1991). One study reported an overall strain/sprain prevalence of 31% per season (McCurdy et al., 2003).
Frequent occurrences of muscle pain (a common symptom of strain) have also been found in orchard work. For example, a study in Japan examining musculoskeletal symptoms in apple and pear work found self-reported neck pain and stiffness ranging from 25–50% of workers in apples and from 40–60% of workers in pears. Sixty-five to 70% of workers in both crops reported stiffness in the shoulder, with roughly a third of apple workers and half of pear workers reporting shoulder muscle pain. Similar rates of neck pain with motion were reported as well (Sakakibara et al., 1995). Calisto (1999) also found an elevated prevalence of pain among fruit growers in the upper and lower back (19% and 57%, respectively), and in the neck and shoulders (both at 38%).
In addition to strain and pain outcomes, long periods of exposure to the ergonomic hazards of awkward posture and weight bearing among orchard workers have been documented (Earle-Richardson et al., 2004; Calisto, 1999). As a proportion of the workday, these periods of exposure are as long, or longer than those found in construction and nursing, two reportedly high-risk occupations (Earle-Richardson et al., 2004).
The New York Center for Agricultural Medicine and Health has developed an ergonomic bucket modification to reduce the load borne by the back, neck and shoulders of apple harvest workers, consisting of a supporting hip belt which redistributes weight from the upper back, neck and shoulders to the lower trunk, a preferable vertical height for weightbearing, and also maintains the load close to the body (Waters et al., 1994; Pheasant, 1991; Page, 1985). The intervention (shown in Fig. 1), is more fully described in a previous issue of this journal (Earle-Richardson et al., 2005), and in a preliminary laboratory EMG study (Earle-Richardson et al., 2006).
As with the laboratory research, it was necessary to use an intermediate endpoint in the development of musculoskeletal strain because there currently exists no objective physical measure of the outcome. However, because it was not feasible to conduct EMG research in the orchard, the development of mechanical methods that could be used in the orchard environment was undertaken.
Detection of muscle fatigue through measurement of changes in morning to afternoon maximum voluntary contraction was selected as an endpoint. According to a model proposed by Armstrong et al. (1993), the development of musculoskeletal strain can be thought of as a sequence of four events: exposure, internal dose, capacity and response. In this context, internal dose is the body's initial response to a given load. One example of internal dose is muscle fatigue. While other capacity factors, such as rest time and overall condition, may ultimately determine whether an individual with a given internal dose develops muscle strain, an intervention that significantly reduces the internal dose can reasonably be called beneficial in preventing or reducing muscle strain. A number of other studies describe a similar process (Clarkson and Hubal, 2002; Proske and Morgan, 2001; Clarkson and Sayers, 1999; Sjogaard and Sogaard, 1998; Green, 1997; Clarkson and Newham, 1995; Brystrom and Fransson-Hall, 1994; Hagberg, 1981).
In the context of this study, fatigue is defined as the pre- to post-exposure decline in maximum performance occurring after a period of exertion (Lanza, 1999). Published fatigue studies of this type measure either time holding a posture, one-time attainment of a maximum reading on a dynamometer or possibly a dichotomous pass/fail metric for performance of weighted or non-weighted tasks (Lee et al., 2001; Nussbaum et al., 2001; Hughes et al., 1999; Vollestad, 1997; Bloswick and Mecham, 1994).
Before being used in a large orchard trial, the sensitivity of each type of performance measure for apple harvest work needed to be evaluated. For the purposes of the current study, a measure deemed effective was one that detected a change in muscle strength occurring over an orchard harvest workday. This methodology is unique in that other published studies take pre- and post-measurements over a relatively short interval of time (no more than 2 h), whereas this method seeks to measure a real work day of actual farm workers (6–8 h). Interventions can thus be evaluated on their ability to reduce one-day muscle fatigue.
Section snippets
Design
The study has two phases: a laboratory phase and an orchard phase. Both phases are experimental in design. Beginning first in the laboratory with volunteers, pre- to post-work muscle strength measures are used to identify extent of muscle fatigue. Successful tests were then subjected to the same study process, using actual farmworkers in the orchard. Table 1 shows the details of the laboratory and orchard evaluation phases.
Hypotheses
Laboratory phase hypothesis: one or more musculoskeletal strength (or
Laboratory phase
In the laboratory, statistically significant fatigue between pre- and post-work measurements was found for two measures: the timed arm hold (35.7% reduction, 95% CI: 21.8–49.6), and the timed spinal extension (31.8% reduction, 95% CI: 23.5–40.0). The other tests were not significant (Table 2). All subjects had an elapsed time of 2 h, and had no warm-up interval.
Orchard phase
Table 3 shows selected demographic and physical characteristics of the study subjects who participated in this phase. The subjects were
Laboratory phase
The laboratory data indicate that two measures are sensitive to one day of orchard harvest work: the timed arm hold (35.71% reduction, 95% CI: 21.81–49.61), and the timed spinal extension (31.75% reduction, 95% CI: 23.54–39.96). Thus, the hypothesis that laboratory measures of muscle fatigue could be identified was found to be valid.
Orchard phase
In contrast, the orchard workers showed a much smaller fatigue effect for the arm hold (11.4% p<.0001) and did not exhibit a significant fatigue effect for either
Conclusions
Throughout the research, 12 different muscle strength measures were evaluated; four of these were timed endurance measures, and eight were maximum contraction measures (employing the dynamometer). While further research is needed to draw any firm conclusions, this preliminary data seems to suggest that endurance measures may be more effective in this setting than maximum strength measures. The fact that these measures diminished in the extent of fatigue detected from the laboratory (with
Acknowledgements
Special thanks to the orchard owners and orchard staff who advised and assisted the research team, the farmworkers who participated in the muscle testing, and the several other individuals who offered their expertise throughout the project: Jim Bittner, Nate Darrow, Cliff de May, Mike Fargione, Gary Fitch, Mac and Mason Forrence, Peter and Seth Forrence, Ron and Ted Furber, Tre Green, Kevin Iungerman, Roger and Charles Lamont, Jim Lamont, Chuck Mead, Al Mulburry, Darrel Oakes, Todd Rogers, Pete
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