The effect of forearm position on elbow flexion strength in nursing,occupational,and physical therapy students

Abstract

BACKGROUND:

Novice nurses, occupational and physical therapist’s injury rates are alarming.

OBJECTIVE:

To test for differences in peak elbow flexion forces (PEFF) by profession using different forearm positions.

METHODS:

Entry-level RN, OT, and PT students performed 3-repetitions of standing PEFF in forearm supination, pronation, and neutral. A one-way repeated measures ANOVA determined the forearm position with the greatest PEFF. A one-way ANOVA assessed differences in PEFF between professions. The alpha level was set at p≤0.05 for all analyses.

RESULTS:

Thirty 30 RN, 25 OT, and 30 PT students (x = 23.27 + /–3.29 yrs.) were studied. A one-way repeated measures ANOVA revealed a significant difference in PEFF between positions (F(2,168) = 144.3, p < 0.0001). A significant (p < 0.0001) pairwise comparison revealed neutral produced the greatest (28.15 + /–12.64 kg) and pronation the least PEFF (17.27 + /–7.40). PEFF was significantly different between position by profession (supination: F(2,82) = 10.14, p < 0.0001; pronation: F(2,82) = 10.33, p < 0.0001; neutral: F(2,82) = 13.39, p < 0.0001). PTs were significantly stronger than OTs and RN students in all forearm positions (p < 0.01).

CONCLUSIONS:

Neutral PEFF was greatest and PT students demonstrated greater PEFF than OT and RN students.

Keywords

Health professional lift functional strength

1 Introduction

In 2017, U.S. workers in the health care and social assistance industry accounted for 35%of reported nonfatal occupational injuries, the highest number of such injuries reported for all private industries [1]. The number of cases (582/100,00 in health care) was two-to-ten times greater than those in agriculture (50/100,000), transportation 216/100,000) and arts (59/100,000) workers while the incidence rate per 100 full-time workers was 4.1, lagging slightly behind agriculture, transportation, and the arts [1].

Alarmingly, the U.S. health care personnel have seven times the national rate of musculoskeletal disorders vs. all private sector workers. [2]. Seventy-five percent of nurses report symptoms of work-related musculoskeletal disorders (WRMSD) in at least one body region within a 12-month period [3]. Other studies of nurses report a higher annual prevalence of 81–95%[4 –9]. A systematic review of physical therapists reveals that up to 90%have WRMSDs during their careers with 50%experiencing WRMSDs within 5-years of initiating practice [9]. Typically, the low back is the most commonly affected body part, however, shoulder/elbow/wrist typically ranks second [9]. In general, female physical therapists and physical therapists working in hospitals have a higher prevalence of WRMSD [9]. WRMSD are associated with PT’s age, gender, specialty and job tasks [9]. Performing manual therapy, lifting and transferring patients are tasks commonly associated with physical therapists developing WRMSD [9]. Eighty-six percent of Korean occupational therapists reported a WRMSD of at least one body site [10]. Occupational and physical therapists face significant risks of injury and have a similar annual incidence rate of WRMSD to each other and to workers employed in heavy manufacturing [11].

A systematic review found that thirty-three percent of musculoskeletal injuries in allied health professionals occurred during patient handling while 32%of these injuries occurred while repositioning patients in bed or catching falling patients [12, 13]. While the low back is often indicated as the area most frequently injured, a recent cross-sectional study of 347 Irish physiotherapists found that the prevalence of injuries to the shoulder, elbow, wrist, finger, and thumb was 10.15%, 5.3%, 7.5%, 2.2%, and 10.75%, respectively [14]. Age and/or experience may be factors as injuries are highly prevalent in younger therapists [9]. On the contrary, shoulder injuries were significantly more prevalent in physical therapists with greater than 10 years of experience [14]. Otherwise injuries rates were similar across age/experience groups [14].

Safe patient handling tasks are complicated by staffing concerns, decreased patient mortality, increased severity of hospital, skilled nursing and rehabilitation patients, increased rates of obesity, and trends for early patient mobility and rapid patient discharge [15]. These challenges require that healthcare workers, specifically nurses, physical and occupational therapists be knowledgeable and confident in proper body mechanics while positioning patients for lifts or during lifting when equipment and/or lift teams are unavailable.

The principles of safe lifting, patient handling and treatment techniques are generally taught in entry-level nursing, occupational and physical therapy education programs. Authors of entry-level texts discuss positioning, primarily focusing on leg and torso/low back positioning during patient lifting/transfers [16 –21]. One author suggested that the acromioclavicular joint should be at 0–45° of flexion during patient transfers, but instruction on proper forearm position was rarely if ever provided [22]. This omission is important as a recent review of WRMSD in nurses suggests that only 27%of all studies have investigated pain in the upper and lower extremities [15]. Only one citation could be found suggesting the use of a supinated grip during patient transfers, however, that statement was not referenced [23]. There is some support for the use of a neutral or supinated forearm position during lifting as it can optimize maximal wrist flexion torque^, elbow flexion strength and steadiness [24 –26]. There is a lack of guidance in the entry level clinical literature for nursing, occupational and physical therapy students regarding proper forearm positioning during patient lifting/transfers, yet there is a clear increased risk of injury for these three professions who are primarily called upon to mobilize patients. Determining optimal forearm position for peak lifting forces during patient lifting may determine a best practice and mitigate injury risk while lifting or transferring patients.

1.1 Objective

The purposes of this investigation were: (1) to determine the forearm position (pronation, neutral, supination) that generated peak elbow flexion force (PEFF) and (2) to identify differences in PEFF in nursing, occupational, and physical therapy students.

2 Methods

2.1 Participants

Following approval by two University Institutional Review Boards, professional students enrolled in nursing (RN), occupational (OT) and physical therapy (PT) degree programs were recruited from local universities via face-to-face meetings and/or email messaging. Subjects were excluded from participation if they had a history of upper extremity (UE) injury diagnosis, trauma or surgical repair or UE tendinopathy within the past 6-months, had acute UE pain or neurologic disorder/injury or prosthetic, or had an upper extremity sprain/strain within the past 30-days. Subjects also completed a PAR-Q questionnaire prior to further testing [27].

2.2 Procedure

Once cleared for participation, subjects rested in a seated posture for 5-minutes prior to having their resting heart rate and blood pressure measured. Those who were tachycardic or hypertensive were deemed ineligible for participation. Eligible subjects provided informed consent and were measured for height and weight. Percent body fat and lean body mass were obtained via bioelectric impedance [28]. Subjects completed 3-trials of grip strength with a grip dynamometer in a neutral forearm position with 10-seconds rest between trials [29, 30].

Subjects performed a standardized, dynamic four-minute upper-extremity warmup prior to assuming a standing position on an isometric lift platform [31]. Subjects stood with slight knee flexion, feet shoulder width apart and malleoli at a consistent mark. Subjects held a specially designed handle allowing for consistent shoulder abduction (0°) in the three forearm positions. The handle was affixed to a calibrated force transducer and to the base of the platform allowing for measurement of PEFF [29]. Handle height was adjusted so that elbow angle could be maintained at 90° of elbow flexion. Subjects were instructed to pull upwards with maximal force for six-seconds. Three repetitions of six-second isometric lifts were carried out with a 20-sec rest between lifts and a one-minute rest between different forearm positions. The order of each set of three repetitions of each lift was randomized for each subject.

2.3 Data analysis

Grip strength, neutral, pronated, and supinated elbow flexion forces were averaged for each set of contractions and these values were used for statistical analysis. Power analysis revealed that 90 subjects would be needed for a statistical power greater or equal to 0.80 with a medium effect size and alpha level of 0.50. Force data was collected in absolute terms (kg) and normalized by lean body mass (force-kg / LBM) to account for the small but different numbers of male subjects in each group [32]. A One-way repeated measures ANOVA (SPSS 25.0) identified the greatest peak elbow flexion force by position for all subjects [33]. A One-way ANOVA was calculated to test for differences in peak elbow flexion force by forearm position between professions. A Pearson correlation coefficient was calculated to determine the relationship between grip strength and peak elbow flexion force. Statistical significance was set at p≤0.05 for all analyses.

3 Results

Eighty-five volunteer subjects (70 female and 15 males) from professional entry-level nursing (30), Occupational Therapy (25) and Physical Therapy (30) programs in a West Texas city participated in the investigation. The genders for each subject group were representative of their respective professions. Ages (OT = 23.6 + /–2.0 yrs; PT 23.2 + /–1.3yrs, RN 23.1 + /–5.1 yrs) were similar and not statistically different across the groups.

The one-way ANOVA revealed that grip strength was significantly greater (F (2,82) = 9.063, p < 0.01) in PT students (38.90±10.51 kg) vs. OT students (29.22±6.43 kg) or RN students (32.25±8.37 kg). RN and OT students were not different (p = .408) in grip strength. Grip strength was highly correlated (p < .000) with peak supination, pronation, neutral elbow flexion force, r = 0.853; r = 0.802; r = 0.854, respectively.

3.1 PEFF by forearm position

The one-way repeated measures ANOVA revealed a statistically significant difference in PEFF between positions (F(2,168) = 144.03, p < 0.0001). Pairwise comparisons revealed force production by forearm position were significantly different (p < 0.0001), for neutral, supination, and pronation PEFF of 28.15 + /–12.64 kg), 23.36 + /–10.53 and 17.27 + /–7.40 kg, respectively.

3.2 Forearm by profession

A significant difference was found between position by profession (supination: F(2,82) = 10.14, p < 0.0001; pronation: F(2,82) = 10.33, p < 0.0001; neutral: F(2,82) = 13.39, p < 0.0001). (Tables 1 2). Physical therapy students were significantly stronger than occupational therapy students and nurses in all forearm positions (p < 0.01) while nursing and occupational therapy students PEFF forces did not differ in any positions.

Table 1
Differences in peak elbow flexion force by professional school and forearm position

Position Greater peak elbow flexion force Compared to p value

Supination Physical Therapy Occupational Therapy p < 0.0001^*

Physical Therapy Nursing p < 0.003^*

Nursing Occupational Therapy p < 0.610

Pronation Physical Therapy Occupational Therapy p < 0.0000^*

Physical Therapy Nursing p < 0.020^*

Nursing Occupational Therapy p < 0.155

Neutral Physical Therapy Occupational Therapy p < 0.0001^*

Physical Therapy Nursing p < 0.004^*

Nursing Occupational Therapy p < 0.107

Position	Greater peak elbow flexion force	Compared to	p value
Supination	Physical Therapy	Occupational Therapy	p < 0.0001^*
	Physical Therapy	Nursing	p < 0.003^*
	Nursing	Occupational Therapy	p < 0.610
Pronation	Physical Therapy	Occupational Therapy	p < 0.0000^*
	Physical Therapy	Nursing	p < 0.020^*
	Nursing	Occupational Therapy	p < 0.155
Neutral	Physical Therapy	Occupational Therapy	p < 0.0001^*
	Physical Therapy	Nursing	p < 0.004^*
	Nursing	Occupational Therapy	p < 0.107

^*Physical Therapy students were significantly stronger than Occupational Therapy or Nursing students.

Table 2

Peak elbow flexion force (kg) in Nursing, Occupational and Physical Therapy students by forearm position

	Supination (mean±sd)	Pronation (mean±sd)	Neutral (mean±sd)
Nursing	21.11±8.75	16.58±6.53	26.63±10.11
Occupational Therapy	18.66±7.58	13.20±5.35	20.49±8.60
Physical Therapy	29.53±11.55^*	21.34±7.78^*	36.05±13.49^*

^*Physical Therapy students were significantly stronger than Nursing or Occupational Therapy in all forearm positions.

4 Discussion

4.1 Main findings

The neutral forearm position generated the greatest elbow flexion force for the combined sample and for the nursing, OT, and PT student groups. PT students expressed slightly more force in each forearm position compared with nursing or OT students. Nursing students expressed slightly more force in each forearm position compared to OT students. Grip strength findings were similar between groups.

4.2 Grip strength and endurance and lifting ability

Since grip strength is involved in isometric elbow force testing and in lifting or transferring patients a brief discussion is warranted. A study of male subjects, maximal grip strength was not significantly different in neutral, and 60° pronated or supinated forearm positions [34]. This might provide a mechanical advantage for the PT students and physical therapists early in their career when mobilizing patients.

Grip strength is greater in standing as the shoulder moves from 0° towards 45° flexion due to increased activity of the flexor carpi ulnaris, flexor carpi radialis and anterior deltoid [33]. It is suggested that during heavy lifting, the elbows be kept close to the body as in this investigation, but elbow flexion angles often change within that range during patient transfers [19, 20]. Grip strength has been found to be significantly greater at 45° vs. 0° of shoulder abduction [34]. Patient transfers involve moving a heavy load (patient) away or toward oneself. However, increased shoulder abduction, while optimizing grip strength might predispose a clinician’s’ upper extremities or back to injury while transferring a patient. Conversely, grip endurance time is greatest at 0° shoulder abduction and 90° elbow flexion as in our investigation [34]. Thus, as a therapist or nurse maintains a lift, one has greater strength and endurance with the shoulder at 0° abduction, 90° elbow flexion, with a neutral forearm and wrist [34]. There is some disagreement in the literature as to optimal elbow flexion angles (0°, 45°, 90°) required to elicit peak grip force, A recent investigation found no difference in grip force angle at 0° to 90° [33].

4.3 Forearm position during lifting

Current findings revealed that at 90° of elbow flexion, forces measured in the neutral forearm position were significantly greater than those during supination or pronation and are supported in the literature [35]. While the biceps brachii, brachioradialis, and pronator teres all flex the elbow, the brachialis is the most voluminous elbow flexor with the greatest peak force and physiological cross-section area [36]. Additionally, the brachioradialis causes full elbow flexion and rotation of the forearm to the near neutral position [35 –37]. Thus, the contribution of these three flexors is a likely explanation for the neutral forearm posture yielding the greatest elbow flexion force [37]. A recently published systematic review concluded that isometric elbow supination strength was greater than pronation strength [37]. These findings support our current findings for the entire sample and each profession.

4.4 Strength differences between student groups

Physical therapy student subjects were significantly stronger than occupational or nursing students while nursing students were slightly but not significantly stronger than occupational therapy students in all three forearm postures. This was not unexpected as average grip strengths of PT, Nursing, and OT students were 38.83, 32.21, and 29.17 kg, respectively. Grip strength is typically used as an indicator of overall strength. Our nursing sample, although weaker than the PT group, had an identical grip strength as a Portuguese nursing sample (32.3 kg) [38]. There is a paucity of data regarding physical fitness levels of PT, OT, or nursing students. A study of Swedish nursing and physical therapy students revealed PT students reported a higher frequency of current physical exercise than nursing students [39]. Interestingly, nursing students reported a higher prevalence rate of neck, shoulder, elbow, upper and low back pain than PT students. PT students reported greater elbow, wrist/hand, hip, knee, and ankle/foot pain than nursing students [40]. In a different investigation, the same author found that 72.2%, 68.9%, and 59.7%of Swedish Nursing, OT, and PT students, respectively reported experiencing back pain sometime in their lives. OT students reported significantly more neck pain (54.1%) vs. nursing (37.1%) or PT (29.9%) students [41]. The most common reports of pain were from the neck, shoulder and low back [41]. These and other findings suggest some students bring upper quadrant and back pain with them upon entering the workforce [40 –42].

4.5 Methodological considerations

An initial concern in data analysis was the unequal number of males within each subsample. However, the gender distribution for occupational therapy and physical therapy samples were within 5%and that of nursing was within 10%of the national average. There was a slightly higher percentage of females within the occupational and physical therapy samples and slightly more male nursing students than the national average. Thus, we believed the gender breakdown of the student samples were representative of the work force. However, since men typically express greater muscle mass and strength than women, elbow force data was normalized by dividing force output by lean body mass prior to statistical analysis [32]. Statistical findings using PEFF/LBM were identical to the findings using and absolute force measure so PEFF findings are presented in kilograms.

4.6 Implications for practice and research

The results from this sample suggest that PT students were 30 %and 55%stronger than occupational therapy and nursing students, respectively during a neutral forearm lifting task. This difference was statistically significant and functionally important. Despite this vast difference in strength, upper limb disorders are common in PT’s, occurring during or shortly after graduation (within 5-years). Increased strength in this student group might be a disadvantage as these professionals might be enlisted to transfer patients more frequently. Additionally, with the demands of full-time employment, and increasing personal responsibilities, all these professionals are likely to become less fit with aging. Thirty-eight percent of PT’s had their first onset or worst upper extremity injury within 5 years of graduation and 2%were injured during training [14, 43]. The most affected body sites for annual prevalence in PTs were shoulder (53.2%), neck (49.4%), and thumbs (46.1%), however, neck (10.8%), shoulder (10.5%) and wrist (7.9%) symptoms produced the most incapacitating conditions [14]. Young Korean OTs (Age 25.6 yrs) had 81.1%, 24.2%and 73.7%shoulder, arm/elbow and hand/wrist/finger WRMD’s, respectively and the shoulder and hand/wrist/finger frequencies were higher than either neck or back complaints [44]. Nurses self-report 37.3%and 34.3%of their absenteeism is due to applying hand/finger force or due to repetitive arm movement [45].

Can student or novice nurses, OTs and PTs prevent WRMSD? A quantitative survey of OTs and PTs asking this question yielded six strategies, including: departmental or organizational, workload & work allocation, work practices, work environment and equipment, physical condition or capacity, and education and training [46]. Under these categories were specific recommendations, including those related to regular staff exercise classes, training and usage of lifting aids, use of therapy assistants and manual handling [46]. A study of 653 Iranian nurses revealed that work body posture had a significant and direct effect via fatigue on musculoskeletal symptoms [47]. In physical therapists, manual therapy techniques, transfers, lifting, prolonged positioning, and repetitive tasks were associated with WRMSD [48].

A systematic review of intervention studies found that supportive evidence for “no-lift” policies and/or the use of technical aids in patient handling was poor to very poor [49]. Therefore, nurses, occupational and physical therapists should receive continual reinforcement about safe work postures, as well as be encouraged to monitor their pre-work and work-related fatigue in an effort to prevent WRMSDs. Since patient handling still occurs, attention to forearm position as part of a comprehensive work-related injury prevention program should be encouraged [46, 47].

Footnotes

Acknowledgments

Thanks to Marissa Jurkis for provision of outstanding library services and to our subjects for their participation. Thanks to Dr. Janelle K. O’Connell for her kind review of this manuscript.

Conflict of interest

There are no conflicts of interest to disclose.

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