1. Introduction
Nowadays, many companies sponsor exercise programs as a strategy to improve economics and employees’ health outcomes. These exercise programs have shown benefits in health, such as increases in well-being and reductions of health risk factors, and work productivity [
1]. These health benefits could be especially important in health care professionals who take care of the rest of the population. However, physical activity levels in healthcare workers are generally low [
2,
3]. The reasons given by most healthcare workers (i.e., >70%) for not exercising were “no time”, “too tired”, “not accessible”, and “no partner” [
3]. Moreover, a study conducted in Taiwan [
2] showed approximately 90% of nurses exercised once a week, and none exercised more than 3 times per week. To try to resolve this situation, some previous studies implemented interventions and indicated that exercise improved the fitness levels and health of healthcare workers [
3,
4,
5]. An exercise program implemented in nurses significantly improved strength levels and cardiopulmonary function [
3]. These results are similar to the results found by Christensen et al. [
4] that focused on 98 female healthcare workers who participated in an intervention program that consisted of diet, physical exercise, and cognitive behavioral training during working hours for one hour weekly. To the best of the authors’ knowledge, research investigating the effects of exercise in healthcare workers is scarce.
Resistance training (RT) is one of the main exercise methods and produces different muscle adaptations depending on the variables that configure the RT stimulus (i.e., load, sets and repetitions, rest duration, exercise type and order, and movement velocity) [
6]. The accumulation of repetitions during RT produces progressive muscle fatigue, and if the subject continues with exercise execution, task failure occurs because volitional fatigue arrives with maximum subject stress and with a maximum rate of perceived exertion (RPE) [
7]. In this sense, there are some RT studies that suggest that performing repetitions to failure would be necessary to enhance maximal muscle mass and strength gains [
8,
9,
10]. However, other RT studies have shown similar and even higher improvements in strength and athletic performance without reaching muscle failure [
11,
12,
13,
14,
15] and with diminished muscle damage, fatigue, and time recovery [
12,
16]. This RT method without reaching muscle failure was defined by González-Badillo and Gorostiaga Ayestarán [
17] as “effort character” (EC). EC was defined as the relationship between the repetitions performed and the repetitions achievable. Then, according to the number of repetitions performed below the maximum in a series, the EC will be different. The EC will be maximized (i.e., 100%) when the subject realizes all the repetitions possible in a series with any load. Therefore, an EC of 50% indicates execution of 50% of the repetitions achievable in a series. Further, RT is oriented to improve adherence to exercise in a sedentary population or with low levels of physical activity or fitness in which the physiological and psychological stress produced during RT must be controlled (e.g., high muscle tension, fatigue, delayed onset muscle soreness, and fear of injury). In this sense, RT programs with moderate EC (e.g., EC 50–70%) may enhance the adherence to exercise but without losing the training adaptations of a higher EC program (e.g., EC 90–100%). Then, RT programs with moderate EC must achieve enough training load to improve one’s physical condition, health, and quality of life. The aim of this study was to determine the effects of two programs of eight-week duration of concurrent training (CT) with different EC over muscle strength (MS), cardiorespiratory fitness (CRF), functional mobility (FM), health-related quality of life (HRQoL), and lipid profile (LP) among hospital workers. We hypothesized that both groups will improve similarly and without significant differences in MS, CRF, FM, HRQoL, and LP.
3. Results
Results for MS, CRF, FM, HRQoL, and LP of both groups are shown in
Table 4,
Table 5 and
Table 6. No significant differences for any variable were detected between the training groups at baseline.
3.1. Adherence to Training Interventions
Attendance of exercise intervention for participants in the EC 50% and EC 100% groups were 81.3% and 63.4%, respectively. There was no statistically significant difference in adherence levels between the groups (p = 0.265).
3.2. Muscle Strength
MS significantly increased across time in EC 50% for leg press machine (p = 0.001; d = 0.74), vertical chest press (p = 0.008; d = 0.38), and lateral pulldown machine (p = 0.004; d = 0.45) and in EC 100% for leg press machine (p = 0.007; d = 0.61), vertical chest press (p = 0.024; d = 0.38), and lateral pulldown machine (p = 0.014; d = 0.31). No significant differences were found between EC 50% and EC 100% after eight weeks of CT for leg press machine (F1,11 = 1.76; p = 0.211; η2 = 0.14), vertical chest press (F1,11 = 0.45; p = 0.516; η2 = 0.04), or lateral pulldown machine (F1,11 = 2.12; p = 0.173; η2 = 0.16).
3.3. Cardiorespiratory Fitness
Regarding peak VO2, EC 50% (p = 0.015) but not EC 100% (p = 0.400) displayed a significant change in VO2peak during the exercise intervention; in addition, the EC 50% group showed a moderate ES (d = 0.64). After the intervention, no significant changes were found between EC 50% and EC 100% for VO2peak (F1,11 = 0.93; p = 0.355; η2 = 0.08).
3.4. Functional Mobility
After eight weeks of CT among hospital workers, participants of EC 50% significantly increased performance of the FRSTST (p = 0.007; d = 1.20) and 30 WT (p = 0.004; d = 0.68) over time. On the other hand, EC 100% participants significantly improved for FRSTST (p = 0.012; d = 1.76) but not for 30 WT (p = 0.080). At the end of the intervention, no significant differences arose between EC 50% and EC 100% for FRSTST (F1,11 = 0.47; p = 0.507; η2 = 0.04) or 30 WT (F1,11 = 0.07; p = 0.802; η2 = 0.01).
3.5. Health-Related Quality of Life
Table 5 shows the scores on HRQoL. None of the groups showed significant changes in PCS or MCS after eight weeks of intervention: EC 50% (
p = 0.256 and
p = 0.099) nor EC 100% (
p = 0.125 and
p = 0.240). After intervention, no significant differences were found between EC 50% and EC 100% for PCS (F
1,10 = 0.19;
p = 0.676; η
2 = 0.02) or MCS (F
1,10 = 1.72;
p = 0.219; η
2 = 0.15).
3.6. Lipid Profile
After eight weeks of intervention, LDL-C levels significantly decreased in EC 50% (p = 0.013; d = 0.48), and HDL-C values significantly increased in EC 100% (p = 0.021; d = 0.24). No significant differences were found between EC 50% and EC 100% after eight weeks of CT for TC (F1,11 = 1.70; p = 0.218; η2 = 0.13), LDL (F1,11 = 0.19; p = 0.668; η2 = 0.02), HDL (F1,11 = 1.05; p = 0.327; η2 = 0.09), or TG (F1,11 = 0.13; p = 0.729; η2 = 0.01).
4. Discussion
The present study examined the adaptations in MS, CRF, FM, HRQoL, and LP for two different eight-week CT programs. The main findings were that both groups significantly improved MS and FM levels but not HRQoL. Moreover, the EC 50% group improved CRF and the LDL-C values of the LP. The EC 100% group improved HDL-C values of the LP. No statistical differences between EC 50% and EC 100% were found in any test despite the fact that EC 50% performed half the volume of the strength workout. However, it is possible that the low adherence of EC 100% (63.4%) may have limited intra- and inter-group differences. To our knowledge, this is the first study investigating CT with different effort character over strength and FM among hospital workers.
In terms of adherence to the exercise program, there were no statistical differences between the EC 50% and EC 100% groups. However, it seems there was a positive trend in the EC 50% group adherence (+17.9%) that may have been due to the better affordable load planification (i.e., half the volume training repetitions). This issue should be deeply investigated because low exercise adherence is one of the biggest problems in hospital workers [
15] and a main limitation factor in the promotion of exercise’s positive benefits and adaptations in health and quality of life.
Our global results are consistent with the findings of Yuan et al. [
15], who implemented an aerobic training program three to five times a week during three months for nurses. They observed significant improvements on hand grip strength, endurance strength of abdominal and back muscles, hamstring flexibility, cardiopulmonary function, and BMI. In comparison, Brox and Froystein [
30] performed a weekly exercise class (i.e., light aerobic exercise, muscle strengthening, and stretching) during a six-month period in employees of a community-based nursing home for the elderly. No differences between the intervention and control groups were found for aerobic fitness, HRQoL, or sickness absence. These results may be due to the low exercise frequency (i.e., once weekly) and the low adherence to the intervention (less than 50%) [
30].
Other multidimensional interventions that included exercise programs showed positive effects in healthcare workers. Tveito and Eriksen [
17] conducted an integrated health program (i.e., physical exercise, stress management training, health information, and ergonomic evaluation of workplace) twice weekly during working hours for nurse personnel. The intervention group reported improvement in health, physical fitness, muscle pain, stress management, maintenance of health, and work situation. Furthermore, Christensen et al. [
16] realized an intervention of 12 months consisting of diet, physical exercise, and cognitive behavioral training during working hours for one to two hours per week in overweight female healthcare workers. The intervention group significantly reduced body mass, BMI, and body fat percentage, but there were no changes in CRF or MS.
To our knowledge, there are no eight-week exercise intervention studies in hospital professionals to which we can compare our results. However, Varela-Sanz, Tuimil, Abreu, and Boullosa [
31] performed an eight-week concurrent training intervention in 35 moderately active sport sciences students and obtained an increase in maximal strength of 17.1% and 40.4% in bench press and half squat, respectively, and a 4.3% increase in VO
2peak levels. Moreover, Fyfe, Bartlett, Hanson, Stepto, and Bishop [
32] applied a concurrent exercise program during eight weeks in 23 recreationally active men and observed improvements of 13.9% and 25.8% in bench press and leg press strength, respectively, and a 4.6% increase in VO
2max. In these exercise intervention studies [
31,
32], strength and VO
2peak levels improved similarly to the present study, with gains in EC 50% and EC 100% groups in vertical bench press of 19.3% and 28.5%, respectively; leg press 46.8% and 34.2%, respectively; and VO
2max improved by 6.3% in EC 50% but only by 1.2% in EC 100%.
RT strength improvements at 1 RM after the eight-week CT program were significant across time with moderate ES values. In the upper limbs with vertical chest press exercise, the EC 50% group showed improvements of +19.3% (ES = 0.38), and the EC 100% group showed +28.5% improvement (ES = 0.38), and with lateral pulldown machine exercise, EC 50% improved +17.5% (ES = 0.45) and EC 100% improved +9.5% (ES = 0.31). Moreover, in lower limbs, the EC 50% showed gains in leg press machine exercise of +46.8% (ES = 0.74), and EC 100% showed improvements of +34.2% (ES = 0.61). Regarding 1 RM values, the improvements observed in the present study are consistent with previous studies investigating CT effects in untrained elderly subjects [
33] and office workers [
34] following similar training programs. However, our results showed that performing repetitions to concentric failure did not provide additional strength increases even in the EC 50% group, who performed strength training workouts with the same intensity (e.g., 70% 1 RM) but with half the volume (e.g., six repetitions over 12 RM) compared to the EC 100% group. Strength training based on repetitions to concentric failure implied longer training sessions, higher neuromuscular fatigue, higher RPE, and discomfort [
8,
12,
35]. In addition, repetitions to concentric failure should not be performed repeatedly over long periods due to the high potential for overtraining and overuse injuries [
36]. Therefore, we believe this type of ST training is not necessary to improve strength gains in this population.
In the present work, most of the MS, CRF, and FM tests reached statistical significance after the intervention in both groups. Most of the tests performed showed moderate to large ES, as displayed in
Table 4. In the rest of the variables in which we did not find significant differences (i.e., HRQoL and LP), we must consider that the participants in our study were healthy subjects, and it could be difficult to obtain significant improvements in only eight weeks. This type of intervention might be more beneficial in unhealthy subjects usually associated with low physical activity levels in which smaller increases in physical activity may produce equal or higher health benefits than in healthy and physically active people [
37].
Regarding CRF, only the EC 50% group experienced significant improvement after exercise intervention (+6.3%), with a moderate ES (ES = 0.64). Several studies have measured CRF in both healthcare [
15,
38] and non-healthcare workers [
34,
39]. All of the interventions showed an improvement in CRF, ranging from 7.2–12.8%. A possible explanation for the low improvement in our study could be that the documented durations of these interventions were considerably longer than ours. These studies were conducted for at least four months and up to a maximum of 12 months, whereas our intervention only lasted eight weeks. This fact, together with our small sample size, could explain the low improvement in CRF.
The exercise program did not significantly increase FM assessed by 30 WT in EC 100% (
p = 0.080); however, the ES in the EC 100% group was large (ES = 0.90) compared to the EC 50% group (ES = 0.68). The FRSTST significantly improved in both groups, with large ES (EC 50% group, ES = 1.20; EC 100%, ES = 1.76). Different studies have measured FM, employing FRSTST and 30 MT in healthy young adults and in a clinical population as well [
25,
26,
40]. According to the age-band specific category for FRSTST provided by Bohannon et al. [
25], our results were 3.3% and 6.2% faster in the EC 50% group and in the EC 100%, respectively. With respect to the 30 WT, reference values for healthy Swedish people aged 40–79 years are 1.16–1.47 m/s [
41]. As a result, maximal speeds were higher in our study, although our participants were overall younger.
None of the training programs showed significant differences throughout the eight weeks of intervention in either of the two HRQoL parameters (i.e., PCS and MCS). Nevertheless, the EC 50% group showed a decrease in MCS with moderate ES (0.61). In comparison, the EC 100% group improved in PCS with a moderate ES (0.56). Our results agreed with those found in the review conducted by Nguyen et al. [
42], in which most of the randomized control trials conducted in healthy office workers reported no differences in HRQoL scores.
Regarding the LP, both the EC 50% and EC 100% groups showed a positive trend in most of the LP variables. The EC 50% group showed a significant improvement in LDL-C values (ES = 0.48) and near-moderate ES in TC (0.50) values. In addition, the EC 100% group showed a significant enhancement in HDL-C values (ES = 0.24). However, it increased TG levels after eight weeks of CT (ES = 0.69), but was always between healthy levels. There is ample evidence demonstrating the effectiveness of both aerobic exercise and resistance exercise in improving LP in different populations [
43]. However, in the case of CT, the evidence is limited, and the results are contradictory, with some research documenting significant improvements in LP and others not [
44]. In the study conducted by Shaw et al. [
45], LDL-C was significantly reduced after 16 weeks of CT in 28 healthy male subjects. However, LeMura et al. [
46] found no significant differences in TC, HDL-C, LDL-C, or TG after 16 weeks of CT. Our participants were healthy subjects with values within the normal ranges at the beginning and end of the intervention. This circumstance and the fact that the intervention lasted only eight weeks may explain why some values improved in a preventive but not statistically significant way.
Finally, lower-level exercise training strategies, such as the EC 50% used in the present study, might not cause acute inflammation by muscle damage but could activate the intracellular quality control system and may prevent chronic inflammation [
45]. Moreover, the maintenance and enhancement of muscle strength by exercise can prevent and improve the metabolic syndrome, the age-related diseases, and the cellular immune function and resistance against infections and cancer [
47].
Our study has limitations that need to be addressed. First, the small sample size affected statistical power, which limited the ability to detect significant differences in several outcome measures. Second, average to poor adherence (i.e., 81.3% for EC 50% and 63.4% for EC 100%) could have contributed to worse outcomes. Third, cardiorespiratory performance could be assessed with direct methods (i.e., gas analyzer) to ensure more accurate values. Finally, the lack of a control group weakens our capacity to draw conclusions.