Introduction

Work ability is defined as an individual’s ability to manage job tasks. This concept is associated with individual factors such as physical and mental capacities, which is also influenced by out-work-life factors (1, 2). Nowadays, maintaining and improving the work ability are important social goals, which has received special attention in the national governmental program of several European countries (3). This subject is considered as a challenge for the health care and rehabilitation systems as well as health providers (4). Work ability as a multifactorial phenomenon depends on many factors that can be evaluated, using work ability index (5).

The work ability index is affected by both physical and mental aspects of work and health status including: diagnosed diseases by physicians, limitations caused in the work due to diseases, and the number of days of sick leave during the past 12 months. Regarding this, planning for the improvement of the work ability should involve the activities aimed to reduce work demands (e.g., time restrictions, employers’ views, providing the facilities for the individual to control his/her work, and ergonomic factors) and enhance health status (e.g., improving the aerobic capacity in employees) (6, 7).

According to a study carried out by Kaleta et al., the job related factors and lifestyle should be considered in future programs to enhance the work ability (8). Today, the lifestyle of most people is going toward immobility and hypo mobility, a serious health problem in developed and developing countries (9-11). There are several prospective studies determining the predictor factors of work ability; however, the role of physical activity has not completely recognized yet (2). According to the professional health care principles, musculoskeletal difficulties are common problems among the personnel, leading to disability and off-works; therefore, the physical exercise can be effective in this regard (7).

Nurminen et al. reported that practicing physical exercise in the work environment once a week slightly improved the females’ perceived work ability in difficult tasks (12). Consequently, it is necessary to determine an acceptable level of physical exercise to maintain and improve the work ability among the personnel (12). The nurses and midwives constitute the largest health care organization; accordingly, more than 80% of the patients receive direct services by this population (13). In many developing countries, the employment of the efficient midwives and nurses is considered as a priority of each health programs (14). With this background in mind, this clinical randomized trial was conducted to evaluate the effect of aerobic exercise on work ability. The purpose of this study is to improve the work ability through increasing the fitness level.

 Materials and Methods

This clinical trial was conducted on the midwives working in the health care centers of Mashhad, Iran in 2013. First, the health care centers and sub-centers (No. 1, 2, and 3, urban centers) as well as the Samen health care centers and sub-centers (No. 1 and 3) were selected, using simple random sampling method. Subsequently, each center was randomly assigned into intervention and control groups. Then, the qualified midwives in these centers were selected based on the purposeful sampling method. Due to the lack of similar study, the sample size was calculated as a pilot sample, using the formula comparing means with safety coefficient of 95% and test power of 80%, which assigned 30 samples into each group (totally 60 cases).

The inclusion criteria were as follows: 1) the written consents to participate in the study, 2) Iranian nationality and Mashhad residency, 3) graduated midwifery degree, 4) no pregnancy, 5) non-menopause, 6) lack of psychological problems leading to admission to psychiatric hospitals, 7) not attending in any sport club and training sessions in the past three months, 8) lack of regular physical exercise, 9) lack of second shift work, 10) work history of one year or more, 11) body mass index of < 30. On the other hand, the exclusion criteria included absence of more than five sessions from the exercise program and dealing with bankruptcy problem, divorce, and loss of family members in the past two months.

The data were collected using the demographic characteristics forms and work ability index questionnaire (WAIQ). The WAIQ was filled in before and after the aerobic exercise by the participants of both groups. First, all of the participants were tested by the researchers according to the Bruce test, using the treadmill (Technogym). Subsequently, the participants whose computed consumption oxygen was more than 10.5 mL/kg/min in the Bruce test (i.e., three folds more than the base) were entered in the study. The intervention group was required to perform aerobic exercise for eight weeks. The Bruce test was implemented to compare the fitness of the participants at the pre- and post-intervention stages. Finally, the work ability scores were compared in the two groups before and after aerobics exercise program. The present study was approved by the Ethics Committee of Mashhad University of Medical Sciences.

The work ability index consists of seven dimensions including: 1) current work ability compared to life time best, 2) work ability in relation to physical and mental demands of the work, 3) number of current diagnosed diseases, 4) work impairment due to disease, 5) sick leave during the past year, 6) prognosis of work ability after two years, and 7) mental resources. The total score of this questionnaire has a range of 7-49 (i.e., low: 7-27, moderate: 28-36, good: 37-43, and excellent: 44-49) (15, 16). The reliability of this questionnaire was evaluated by Ehsanollah (2011), using the test-retest method. According to the test-retest results, the correlation coefficient between the items ranged from 0.74-0.88, which indicated an acceptable durability level (17). The reliability of this questionnaire was also calculated in the current study using internal homogeneity, which rendered the Cronbach’s alpha coefficient of 082.

This exercise program, entailing 24 sessions (three sessions a week), was conducted outside normal working hours (i.e., from 6-6.45 p.m.) in the energy management club under the supervision of an exercise coach (MSc of physical education) and the researchers during July-October 2013. Every session lasted 45 min, which consisted of three stages including: warm-up stage (i.e., all types of walking, slow running, stretching exercises, and dancing for 15-25 min), aerobic exercise including slow walking and jogging (lasting 5 min in the first session and reaching to 20 min in the last session), and cooling-down stage (i.e., stretching exercises and walking for 10 min). Whereas the exercise time was fixed, the exercise load increased based on the exercise speed and severity (increasing the jogging distance). Furthermore, the activity duration was increased by reducing the resting time between the repeats or shortening the warm-up time. The maximum consumed oxygen increased from 30-60% over eight weeks.

 Results

According to the results of the study, the mean age of the participants was 41.2±5.1 years (age range:27-49 years). Furthermore, 86.7% and 86.7% of the participants in the intervention and control groups were married, respectively. Most of the samples in the control (86.7%) and intervention groups (86%) had the Bachelor of Science degree. In addition, 100% and 93.3% of the participants in the control and intervention groups had average economic level, respectively. Most of the subjects in the control and intervention groups were officially employed (76.7% and 80%, respectively).

The means of work history were 14.8±6.5 and 15.l7±5.3 years in the control and intervention groups, respectively. Additionally, 63.3% and 70.3% of the participants in the control and intervention groups were working in the Midwifery Department, respectively. Before the intervention, the means of maximum computed consumed oxygen levels according to the Bruce test were 23.4±6.8 and 24.5±7.4 mL/kg/min in the intervention and control groups, respectively.

Furthermore, the participants in the two groups were homogeneous in terms of such variables as age (P=0.290), marital status (P=1.000), literacy level (P=0.757), economic status (P=0.355), type of employment (P=0.974), work history (P=0.572), unit of service (P=0.584), and maximum consumed oxygen (P=0.691) at the pre-intervention stage. Before the intervention, the total means of the perceived work ability were 36.4±5.3 and 36.9±5.0 in the control and intervention groups, respectively. The results of the Mann-Whitney U test showed that there was no statistically significant difference between the two groups regarding the perceived work ability scores (P=0.722), indicating that the two group were homogenous in terms of the work ability.

However, the independent t-test revealed a statistically significant difference between the two groups regarding the increase of the work ability mean scores in the intervention group (P=0.004). Furthermore, the paired sample t-test indicated no statistically significant difference between the pre- and post-inter-vention work ability scores of the control group (P=0.963). Nevertheless, according to the Wilcoxon test, this value was found to be significantly different between the two stages in the intervention group, revealing an increase in the work ability after the intervention (P<0.0001; Table 1).