Association Between Self-Perceived Physical Fitness Assessed Using the International Fitness Scale (IFIS) and Pregnancy-Related Low Back Pain in Physically Active Pregnant Women

Abstract

Background and Objectives: Pregnancy-related low back pain (PLBP) is one of the most frequent musculoskeletal complications during pregnancy and may negatively affect physical function, occupational performance, and quality of life. Although regular physical activity (PA) is recommended during pregnancy, the relationship between self-perceived physical fitness (SPPF) and PLBP remains insufficiently explored. The aim of this study was to analyze the association between SPPF assessed using the International Fitness Scale (IFIS) and PLBP in a cohort of physically active pregnant women. Materials and Methods: A secondary analysis of a prospective cohort study including 147 physically active pregnant women was performed. All participants fulfilled the World Health Organization recommendations for PA during pregnancy (≥600 MET·min/week). PA was assessed using the International Physical Activity Questionnaire (IPAQ), whereas SPPF was evaluated using the IFIS. PLBP was assessed using structured questionnaires and the Visual Analog Scale (VAS). Multivariable logistic regression analyses were performed to evaluate independent associations between IFIS scores and PLBP. Results: PLBP was reported by 95 women (64.6%). During pregnancy, women without PLBP showed significantly higher IFIS scores across all evaluated fitness dimensions compared with women with PLBP (all p < 0.05). Women with PLBP additionally exhibited significant reductions in perceived speed/agility and flexibility compared with prepregnancy values. In multivariable analyses, higher global IFIS scores during pregnancy were independently associated with lower odds of PLBP (adjusted OR: 0.30; 95% CI: 0.15–0.60; p < 0.001). No significant associations were observed between IFIS scores and occupational interruption, umbilical artery pH, or instrumental delivery. Conclusions: Lower SPPF assessed using the IFIS was associated with PLBP in physically active pregnant women. Higher IFIS scores during pregnancy were independently associated with lower odds of PLBP, highlighting the potential clinical relevance of SPPF beyond PA volume alone. Given its simplicity, low cost, and ease of administration, the IFIS may constitute a practical tool for the assessment of SPPF during routine prenatal care. However, prospective studies are needed to clarify the temporal relationship between SPPF and PLBP and to determine its potential predictive value.

1. Introduction

Pregnancy-related low back pain (PLBP) affects nearly half of pregnant women worldwide, with some studies reporting prevalence estimates exceeding 70%, making it one of the most common musculoskeletal complications during pregnancy and an important source of clinical, functional, and socioeconomic burden [1]. Available evidence indicates that both the prevalence and severity of PLBP tend to increase progressively throughout gestation, particularly during the second and third trimesters [2,3,4]. In addition to pain itself, PLBP may substantially interfere with maternal daily functioning, negatively affecting mobility, sleep quality, occupational activities, emotional well-being, and health-related quality of life [5,6,7]. Furthermore, PLBP has been associated with increased rates of sick leave and work-related absenteeism during pregnancy, reinforcing its socioeconomic impact [8,9].

Despite its high prevalence and clinical relevance, PLBP frequently remains underrecognized and undertreated during routine prenatal care. Many pregnant women consider PLBP to be an expected and inevitable consequence of pregnancy and therefore do not seek medical evaluation or treatment [10]. Recent findings from our prospective cohort of physically active pregnant women additionally showed that a substantial proportion of women with PLBP did not seek medical consultation despite experiencing clinically relevant functional and emotional repercussions [11]. PLBP may also have indirect obstetric relevance if pain leads women to reduce physical activity (PA) or adopt prolonged rest during gestation. This is clinically important because lower PA levels and increased sedentary behavior during pregnancy have been associated with a higher risk of hypertensive disorders of pregnancy, including gestational hypertension and preeclampsia, as well as with less favorable delivery outcomes, including higher cesarean delivery rates [12,13,14]. In this context, both international public health guidelines and professional obstetric associations currently support regular PA and exercise during pregnancy because of their recognized maternal and fetal health benefits [15,16,17,18].

In line with current international recommendations, exercise has been proposed as an important non-pharmacological strategy for the prevention and conservative management of PLBP [19,20,21]. Evidence from systematic reviews and meta-analyses indicates that exercise interventions, including supervised modalities such as aquatic exercise and Pilates, may reduce pain severity, improve functional capacity, and enhance quality of life during pregnancy [4,20,21,22]. However, most previous studies have primarily focused on PA participation or exercise volume, whereas considerably less attention has been paid to the potential role of physical fitness and self-perceived physical fitness (SPPF) during pregnancy [23,24].

Beyond PA participation itself, physical fitness has emerged as a potentially relevant factor influencing maternal health and functional adaptation during pregnancy. Physical fitness encompasses several components, including cardiorespiratory fitness, muscular strength, speed-agility, and flexibility, all of which may be clinically relevant during pregnancy [24]. In pregnancy, physical fitness may be particularly relevant because adequate muscular strength, flexibility, postural control, and cardiorespiratory capacity could theoretically contribute to better lumbopelvic stabilization, lower biomechanical overload, and improved tolerance to the physiological and postural changes associated with gestation [25]. However, evidence specifically evaluating the relationship between SPPF and PLBP remains scarce. The International Fitness Scale (IFIS), originally developed within the European Healthy Lifestyle in Europe by Nutrition in Adolescence (HELENA) project in 2011, is a brief self-reported instrument designed to assess SPPF, including overall physical fitness, cardiorespiratory fitness, muscular strength, speed-agility, and flexibility [26]. The IFIS has demonstrated acceptable validity and reliability and has been increasingly used in epidemiological and clinical research because of its practicality, low cost, and ease of administration [27].

In pregnant populations, the IFIS has demonstrated adequate validity and has been associated with several clinically relevant maternal outcomes, including better health-related quality of life among women with higher SPPF levels [28]. Similarly, a previous study from the GESTAFIT (Gestation and Fitness). Project reported that higher SPPF during pregnancy was cross-sectionally associated with lower bodily pain, lower lumbar pain, and reduced pain-related disability, although these studies were not specifically restricted to cohorts composed exclusively of physically active pregnant women [29]. In addition, better IFIS scores have been associated with lower pregnancy-related symptom burden and improved health-related outcomes during pregnancy [30,31]. Likewise, higher SPPF during pregnancy has also been associated with better emotional well-being and lower levels of psychological distress, further supporting the multidimensional relevance of physical fitness assessment during gestation [32]. Collectively, these findings suggest that SPPF assessed using the IFIS may represent a clinically relevant marker of musculoskeletal and functional status during pregnancy. To the best of our knowledge, no previous study has specifically evaluated the relationship between IFIS-assessed physical fitness and PLBP in a cohort composed exclusively of physically active pregnant women. Therefore, the present study is the first to specifically examine the association between SPPF assessed using the IFIS and PLBP in this specific population. In this context, the aim of the present study was to analyze the association between SPPF assessed using the IFIS and PLBP in a cohort of physically active pregnant women. Secondary objectives included evaluating the relationship between specific IFIS dimensions and the functional impact associated with PLBP, as well as exploring potential associations between IFIS scores and selected obstetric and perinatal outcomes.

2. Materials and Methods

2.1. Study Design and Setting

This study was carried out at La Moraleja University Hospital (Madrid, Spain). The investigation represents a secondary analysis derived from a previously published prospective cohort study involving physically active pregnant women (n = 147), originally designed to evaluate the incidence and clinical profile of PLBP during gestation [11]. The present secondary analysis specifically focused on the relationship between SPPF assessed using the International Fitness Scale (IFIS) and PLBP in women fulfilling current World Health Organization (WHO) recommendations for PA during pregnancy.

Participants were recruited from a specialized first-trimester obstetric clinic between 11 and 13 + 6 weeks of gestation. All women had low-risk singleton pregnancies and routinely received standardized recommendations encouraging regular physical exercise throughout pregnancy as part of routine antenatal care. The study was conducted between October 2023 and June 2025. Data collection combined prospective obstetric follow-up with postpartum assessment of self-reported variables. Obstetric and perinatal outcomes were prospectively obtained from electronic medical records, including gestational age at delivery, mode of delivery, neonatal birth weight, Apgar scores at 1 and 5 min, umbilical artery pH, and neonatal admission when applicable. Because these variables were extracted directly from hospital records, they were not subject to participant recall bias. In contrast, information regarding PLBP characteristics, PA levels during pregnancy, and SPPF assessed using the IFIS questionnaire was collected postpartum through structured self-report interviews. Consequently, although the cohort follow-up and obstetric outcome assessment were prospective, part of the exposure assessment incorporated a retrospective component.

Before enrollment, all participants received oral and written information regarding the study objectives and procedures and subsequently signed written informed consent forms. Participation was voluntary, and all women were informed of their right to withdraw consent at any time during the investigation. The study protocol was approved by the Research Ethics Committee of La Princesa University Hospital (Madrid, Spain) (approval No. 5365).

2.2. Study Population

2.2.1. Inclusion Criteria

Women were considered eligible if they were ≥18 years of age and presented a low-risk singleton pregnancy with normal obstetric evolution. Additional eligibility criteria included regular participation in PA during the six months preceding pregnancy, at recruitment, and throughout pregnancy, as well as attendance at the standardized first-trimester obstetric evaluation and ultrasound examination. PA status was established according to the WHO recommendations for PA during pregnancy [15], which advise at least 150 min/week of moderate-intensity aerobic exercise or an equivalent combination of moderate- and vigorous-intensity activity, corresponding to a minimum of 600 metabolic equivalent task minutes per week (MET·min/week). PA levels were evaluated using the short version of the International Physical Activity Questionnaire (IPAQ) [33]. The IPAQ has been extensively used in pregnant populations and has shown acceptable reproducibility in gestational settings [34], in addition to being previously validated in the Spanish adult population [35].

Regarding PA assessment, PA was assessed both during the first-trimester face-to-face visit and during the postpartum telephone interview. In both evaluations, participants were asked to report PA corresponding to a typical week rather than the conventional IPAQ “last 7 days” framework. During the initial recruitment visit, women reported habitual PA during the six months preceding pregnancy and at the beginning of gestation. Subsequently, during the postpartum interview, participants retrospectively reported their usual PA patterns throughout pregnancy. To facilitate consistency in PA reporting, all participants had previously completed the IPAQ during the first trimester in-person assessment and were informed that PA during pregnancy would be reassessed after delivery.

2.2.2. Exclusion Criteria

Women were excluded if, at recruitment or at any time during pregnancy, they presented any obstetric complication, pregnancy-related disorder, or acute or chronic medical condition that could limit, interfere with, or contraindicate the safe performance of physical exercise during pregnancy. This included musculoskeletal, cardiovascular, neurological, or other clinically relevant diseases. Participants who failed to meet WHO recommendations for PA either during pregnancy or during the six months before conception were also excluded. Specifically, women reporting <150 min/week of moderate-intensity PA, corresponding to <600 MET·min/week, were not considered eligible for inclusion. Consequently, the final study sample consisted exclusively of physically active pregnant women.

2.3. Instruments

At the time of recruitment, all participants received standardized written educational material regarding PA during pregnancy. The dossier included evidence-based information describing the maternal, fetal, neonatal, and infant health benefits associated with regular exercise during gestation, together with practical recommendations concerning the appropriate frequency, duration, intensity, and modalities of PA during pregnancy. The information package also summarized absolute and relative contraindications to exercise, warning symptoms requiring interruption of PA, activities discouraged during pregnancy, and general recommendations intended to reduce or prevent PLBP.

2.3.1. Ad Hoc Questionnaire

Data collection was conducted using a specifically designed ad hoc questionnaire developed for the purposes of the present investigation. During the face-to-face first-trimester assessment performed at recruitment, information was obtained regarding sociodemographic characteristics, medical and obstetric history, lifestyle-related variables, and anthropometric data. As no previously validated Spanish or international questionnaire was identified that adequately covered all clinical and contextual variables relevant to the objectives of this study, a tailored instrument was created. The questionnaire items were developed following a review of the available literature on PLBP and were selected to cover the main clinical, functional, and contextual domains relevant to the objectives of the study. The preliminary version of the questionnaire was reviewed by obstetric clinicians and researchers with experience in questionnaire development, who evaluated the relevance, clarity, and clinical applicability of each item to ensure adequate content validity. No formal pilot validation process was carried out before study implementation.

The ad hoc questionnaire was specifically designed to obtain a detailed clinical description of PLBP and its perceived repercussions during gestation. The instrument collected information regarding pain characteristics such as onset, duration, irradiation, aggravating factors, perceived triggering factors, and associated functional limitations affecting daily activities including occupational tasks, sleep quality, and walking capacity. Additional information was gathered regarding emotional repercussions, healthcare consultation, and participants’ perceptions of the effectiveness of different management approaches. The questionnaire was conceived primarily for descriptive and exploratory purposes, aiming to capture the clinical and contextual experience of PLBP rather than to establish formal diagnostic categories or standardized disability classifications. Consequently, specific disability scales, such as the Oswestry Disability Index [36], were not incorporated into the study protocol. Although these instruments have been extensively used in chronic low back pain populations [37], they may not fully reflect pregnancy-specific pain patterns, gestational temporal variability, contextual aggravating factors, or obstetric-related functional limitations relevant to the objectives of the present investigation.

2.3.2. Physical Activity Assessment

During the same first-trimester face-to-face assessment, PA performed during the six months before conception was evaluated using the short-form IPAQ. These data were obtained to characterize habitual prepregnancy PA patterns and to explore potential differences between prepregnancy and gestational PA levels, as well as their possible associations with the presence and intensity of PLBP.

After delivery, all participants underwent a structured postpartum telephone interview. At this assessment, PA performed throughout pregnancy was reassessed using the short-form IPAQ. IPAQ scores were expressed as MET·min/week according to the standardized IPAQ scoring protocol. Additional information regarding PLBP was collected through a structured questionnaire that included variables related to pain location, frequency, duration, clinical characteristics, aggravating factors, therapeutic strategies, and participants’ perceived response to different management approaches. Because recommendations and treatment strategies for PLBP were not standardized across healthcare professionals, management-related variables were collected exclusively for descriptive purposes and were not included in the main analytical models. Participants were also asked about the perceived usefulness of the educational information dossier and whether it had influenced their motivation to remain physically active during pregnancy. However, these data were considered secondary to the principal objectives of the study and are therefore not reported in detail.

2.3.3. IFIS Assessment

SPPF was assessed using the IFIS, a brief self-report instrument that evaluates five dimensions of SPPF, including overall physical fitness, cardiorespiratory fitness, muscular strength, speed/agility, and flexibility, using a five-point Likert scale scored as 1 = very poor, 2 = poor, 3 = acceptable, 4 = good, and 5 = very good [27]. At the first-trimester face-to-face assessment, participants retrospectively reported their SPPF before pregnancy using the IFIS questionnaire. Subsequently, during the postpartum telephone interview, women were asked to retrospectively assess their SPPF throughout pregnancy using the same instrument. Participants were instructed to provide an overall evaluation of their SPPF across pregnancy as a whole rather than referring to any specific trimester or gestational period. The IFIS has previously demonstrated acceptable validity in pregnant populations [28].

2.3.4. Pain Assessment

Pain intensity was assessed using a 0–10 Visual Analog Scale (VAS), where higher values represented greater pain severity [38]. Pain evaluations were obtained for four body positions: sitting, standing, supine position, and lateral decubitus. During the first-trimester in-person assessment, participants received the VAS in printed numerical format and were instructed to retain the scale for use during the subsequent postpartum telephone interview in order to maintain consistency in pain reporting across evaluations. Although data collection was performed through different assessment modalities, the numerical format of the scale remained identical throughout the study. PLBP was defined as pain located between the twelfth rib and the gluteal fold, with or without irradiation to the lower limbs.

2.4. Sample Size

Given the nature of the present investigation as a predefined secondary analysis derived from a previously established cohort, the design, primary characteristics, and sample size of which have been previously reported [11], the available sample size (n = 147) was predetermined by the original study design. Therefore, no additional sample size calculation was performed for the present analysis. Accordingly, the available sample was used to address the exploratory objectives of the present secondary analysis, consistent with the design of the previously published cohort.

2.5. Statistical Analysis

Distributional properties of continuous variables were assessed through visual inspection of histograms and Q–Q plots. Quantitative variables are presented as mean ± standard deviation (SD), whereas categorical variables are expressed as frequencies and percentages. Comparisons between women with and without PLBP were performed using the independent-samples Student’s t-test for continuous variables and the Chi-square (χ²) test or Fisher’s exact test for categorical variables, when appropriate. Because some IFIS dimensions showed slight deviations from normality based on visual inspection of histograms and Q–Q plots, Student’s t-test was considered appropriate given its well-established robustness to mild departures from normality in moderately sized samples. In addition, sensitivity analyses using the Mann–Whitney U test were conducted for the principal between-group comparisons, yielding findings consistent with the primary analyses, thereby supporting the robustness of the statistical results. Within-group comparisons between prepregnancy and pregnancy IFIS scores were performed using paired-samples Student’s t-tests. Correlations between selected IFIS dimensions and exploratory perinatal variables were assessed using Spearman’s rank correlation coefficient (ρ), given the non-normal distribution of some exploratory variables. Finally, multivariable logistic regression analyses were performed to evaluate the independent association between SPPF and the presence of PLBP after adjustment for clinically relevant covariates. Covariates were selected a priori based on previous literature and clinical reasoning because of their potential role as clinically relevant confounders. These included maternal age, prepregnancy body mass index (BMI), standing occupational posture, and PA level during pregnancy. Multicollinearity among the predictors was assessed using the Variance Inflation Factor (VIF) and tolerance. Adjusted odds ratios (ORs) with 95% confidence intervals (95% CIs) were calculated. All statistical analyses were performed using R software (version 4.3.2; R Foundation for Statistical Computing, Vienna Wien, Austria.). Statistical significance was established at p < 0.05.

3. Results

3.1. Study Population and Self-Perceived Physical Fitness

The final cohort consisted of 147 physically active pregnant women who fulfilled the WHO recommendations for PA during pregnancy (≥600 MET·min/week). PLBP was reported by 95 women (64.6%), whereas 52 women (35.4%) did not report PLBP. Women without PLBP were older than those with PLBP (35.2 ± 3.6 vs. 33.5 ± 4.2 years; p = 0.011). Compared with prepregnancy values, perceived speed/agility significantly decreased during pregnancy (p < 0.001), whereas no significant changes were observed in the remaining IFIS dimensions (

Table 1. Self-perceived physical fitness before and during pregnancy assessed using the IFIS questionnaire (n = 147).

IFIS Dimension	Before Pregnancy Mean ± SD	During Pregnancy Mean ± SD	p Value
General physical fitness	3.54 ± 0.76	3.63 ± 0.80	0.267
Cardiorespiratory fitness	3.51 ± 0.74	3.48 ± 0.73	0.645
Muscular strength	3.46 ± 0.77	3.47 ± 0.80	0.826
Speed/agility	3.53 ± 0.68	3.24 ± 0.79	<0.001
Flexibility	3.56 ± 0.99	3.44 ± 0.96	0.066

IFIS: International Fitness Scale; IFIS score interpretation: 1 = very poor; 2 = poor; 3 = acceptable; 4 = good; 5 = very good.

).

3.2. SPPF According to PLBP Status

During pregnancy, women without PLBP showed significantly higher IFIS scores across all evaluated fitness dimensions than women with PLBP (all p < 0.05) (

Table 2. Self-perceived physical fitness during pregnancy according to pregnancy-related low back pain status.

IFIS Dimension	PLBP (n = 95) Mean ± SD	No PLBP (n = 52) Mean ± SD	p Value
General physical fitness	3.51 ± 0.81	3.85 ± 0.74	0.012
Cardiorespiratory fitness	3.37 ± 0.74	3.67 ± 0.67	0.013
Muscular strength	3.36 ± 0.79	3.67 ± 0.78	0.023
Speed/agility	3.13 ± 0.80	3.46 ± 0.72	0.011
Flexibility	3.28 ± 0.96	3.71 ± 0.88	0.008

IFIS: International Fitness Scale; IFIS score interpretation: 1 = very poor; 2 = poor; 3 = acceptable; 4 = good; 5 = very good; PLBP: Pregnancy-related low back pain.

).

3.3. Multivariable Logistic Regression Analysis

A multivariable logistic regression analysis was performed to evaluate the independent association between SPPF during pregnancy and PLBP after adjustment for maternal age, prepregnancy BMI, occupational posture during work activity, and PA level during pregnancy. Higher global IFIS scores during pregnancy were independently associated with lower odds of PLBP (adjusted OR: 0.30; 95% CI: 0.15–0.60; p < 0.001). Maternal age was also significantly associated with lower odds of PLBP (adjusted OR: 0.87; 95% CI: 0.79–0.96; p = 0.006), whereas prepregnancy BMI, standing occupational posture during work activity, and PA level during pregnancy were not significantly associated with PLBP in the adjusted model (

Table 3. Multivariable logistic regression model for pregnancy-related low back pain.

Predictor	Adjusted OR	95% CI	p Value
Global IFIS score during pregnancy	0.30	0.15–0.60	<0.001
Maternal age	0.87	0.79–0.96	0.006
Prepregnancy BMI	1.00	0.90–1.12	0.940
Standing occupational posture	1.00	0.34–2.91	0.996
Physical activity during pregnancy (per 500 MET·min/week)	1.07	0.88–1.31	0.482

OR: odds ratio; CI: confidence interval; BMI: body mass index; MET: metabolic equivalent of task; IFIS: International Fitness Scale.

). No relevant multicollinearity was identified among the predictors included in the final model, with VIF values ranging from 1.03 to 1.17 and tolerance values ranging from 0.851 to 0.972.

3.4. Changes in SPPF Before and During Pregnancy According to PLBP Status

Women with PLBP experienced significant reductions in perceived speed/agility (p < 0.001) and flexibility (p = 0.014) during pregnancy compared with prepregnancy values. No statistically significant changes were observed in women without PLBP (

Table 4. Comparison of self-perceived physical fitness before and during pregnancy according to pregnancy-related low back pain status.

IFIS Dimension	Before Pregnancy PLBP	During Pregnancy PLBP	p Value	Before Pregnancy No PLBP	During Pregnancy No PLBP	p Value
General physical fitness	3.49 ± 0.78	3.51 ± 0.81	0.905	3.63 ± 0.70	3.85 ± 0.74	0.109
Cardiorespiratory fitness	3.45 ± 0.75	3.37 ± 0.74	0.342	3.61 ± 0.71	3.67 ± 0.67	0.666
Muscular strength	3.41 ± 0.77	3.36 ± 0.79	0.503	3.54 ± 0.75	3.67 ± 0.78	0.180
Speed/agility	3.53 ± 0.72	3.13 ± 0.80	<0.001	3.54 ± 0.60	3.46 ± 0.72	0.498
Flexibility	3.49 ± 0.97	3.28 ± 0.96	0.014	3.69 ± 1.01	3.71 ± 0.88	0.875

IFIS: International Fitness Scale; IFIS score interpretation: 1 = very poor; 2 = poor; 3 = acceptable; 4 = good; 5 = very good; PLBP: Pregnancy-related low back pain.

).

3.5. Exploratory Occupational Impact According to IFIS Scores

Exploratory subgroup analyses were performed according to the cohort median global IFIS score during pregnancy. Among women with PLBP, 29 participants interrupted professional activity because of pain symptoms, with a mean sick leave duration of 9.4 ± 6.7 weeks, ranging from 0.5 to 28 weeks. No statistically significant differences in IFIS scores were observed according to occupational interruption status (

Table 5. IFIS scores during pregnancy according to occupational impact of pregnancy-related low back pain.

IFIS Dimension	Occupational Interruption Due to PLBP (n = 29) Mean ± SD	Continued Working Despite PLBP (n = 66) Mean ± SD	p Value
Global IFIS score	3.28 ± 0.63	3.35 ± 0.67	0.601
General physical fitness	3.34 ± 0.90	3.58 ± 0.77	0.234
Cardiorespiratory fitness	3.34 ± 0.72	3.38 ± 0.76	0.836
Muscular strength	3.41 ± 0.68	3.33 ± 0.85	0.626
Speed/agility	3.03 ± 0.78	3.17 ± 0.81	0.456
Flexibility	3.24 ± 0.95	3.30 ± 0.98	0.774

IFIS: International Fitness Scale; IFIS score interpretation: 1 = very poor; 2 = poor; 3 = acceptable; 4 = good; 5 = very good; PLBP: Pregnancy-related low back pain.

).

3.6. Exploratory Perinatal and Delivery Outcomes According to IFIS Scores

Exploratory analyses were also performed to assess the association between SPPF during pregnancy and selected delivery and perinatal outcomes. No statistically significant associations were observed between IFIS scores and fetal umbilical artery pH or instrumental delivery (

Table 6. Correlation between IFIS scores during pregnancy and fetal umbilical artery pH.

IFIS Dimension	Spearman (ρ)	p Value
Global IFIS score.	0.15	0.352
General physical fitness	−0.09	0.591
Cardiorespiratory fitness	0.18	0.266
Muscular strength	−0.04	0.824
Speed/agility	0.07	0.646
Flexibility	0.27	0.094

IFIS: International Fitness Scale; ρ: Spearma’s rank correlation coefficient.

and

Table 7. IFIS scores during pregnancy according to instrumental delivery.

IFIS Dimension	Instrumental Delivery (n = 16) Mean ± SD	Non-Instrumental Delivery (n = 131) Mean ± SD	p Value
Global IFIS score	3.55 ± 0.50	3.44 ± 0.64	0.421
General physical fitness	3.81 ± 0.66	3.60 ± 0.82	0.254
Cardiorespiratory fitness	3.56 ± 0.81	3.47 ± 0.73	0.655
Muscular strength	3.75 ± 0.68	3.44 ± 0.81	0.104
Speed/agility	3.25 ± 0.68	3.24 ± 0.80	0.976
Flexibility	3.38 ± 0.72	3.44 ± 0.99	0.737

IFIS: International Fitness Scale; IFIS score interpretation: 1 = very poor; 2 = poor; 3 = acceptable; 4 = good; 5 = very good.

).

4. Discussion

The present study evaluated the association between SPPF assessed using the IFIS and PLBP in a cohort composed exclusively of physically active pregnant women. The principal findings were that women with PLBP exhibited significantly lower IFIS scores across all evaluated fitness dimensions during pregnancy, including general physical fitness, cardiorespiratory fitness, muscular strength, speed/agility, and flexibility. Moreover, higher global IFIS scores during pregnancy remained independently associated with lower odds of PLBP after adjustment for maternal age, prepregnancy BMI, occupational posture during work activity, and PA levels during gestation. Women with PLBP additionally demonstrated significant reductions in perceived speed/agility and flexibility during pregnancy compared with prepregnancy values, whereas no significant changes were observed among women without PLBP. In contrast, exploratory analyses evaluating occupational and selected obstetric and perinatal outcomes did not demonstrate statistically significant associations between IFIS scores and occupational interruption, fetal umbilical artery pH, or instrumental delivery.

These findings are consistent with existing evidence suggesting that better SPPF during pregnancy may be associated with lower pain burden and improved maternal well-being [28]. Similarly, previous evidence evaluating self-rated health during pregnancy has shown that better maternal self-rated health is associated with more favorable psychological functioning and objective health indicators [39]. In addition, investigations from the GESTAFIT Project demonstrated that higher IFIS scores during pregnancy were associated with lower pain-related burden, reduced pain-related disability, better health-related quality of life, and improved emotional well-being during gestation [28,29,32]. Importantly, unlike previous IFIS-related pregnancy studies performed in general obstetric populations, including the GESTAFIT cohort, the present investigation focused exclusively on physically active pregnant women who fulfilled current WHO recommendations for PA during pregnancy. This distinction is clinically relevant because previous IFIS-related studies included substantial proportions of women who did not achieve recommended PA levels during gestation. In the GESTAFIT cohort, for example, only approximately 22% of participants fulfilled physical recommendations during pregnancy [29]. In contrast, all participants in the present cohort maintained PA levels above the minimum recommended thresholds, thereby reducing the potential confounding influence of sedentary behavior. Consequently, the observed associations indicate that lower SPPF is associated with PLBP even among women who meet current PA recommendations during gestation.

The present findings also reinforce the concept that SPPF during pregnancy may reflect broader aspects of musculoskeletal function and maternal well-being beyond PA volume alone. Previous analyses from the GESTAFIT Project showed that higher SPPF (assessed using the IFIS) were associated not only with lower lumbar pain intensity, but also with reduced pain-related disability and better perceived health status during pregnancy [28,29]. In this context, the present results further support the association between lower SPPF and PLBP, even in women who maintain adequate PA levels throughout gestation according to current WHO recommendations.

From a physiological perspective, several mechanisms could potentially explain these findings. Pregnancy is associated with substantial biomechanical and postural adaptations, including anterior displacement of the center of gravity, increased lumbar lordosis, ligamentous laxity, and progressive overload of lumbopelvic structures. From a biomechanical perspective, lower muscular strength, reduced flexibility, impaired postural control, and poorer overall physical conditioning may be associated with reduced lumbopelvic stabilization and lower tolerance to gestational biomechanical demands [21,25]. Likewise, previous studies have suggested that exercise interventions focused on stabilization, strengthening, and low-impact exercise modalities may contribute to reducing the severity and functional impact of PLBP [19,20]. The observed reductions in perceived speed/agility and flexibility among women with PLBP may therefore reflect greater impairment in functional adaptation to the physical demands of gestation, greater movement-related limitation, and reduced confidence in dynamic lumbopelvic control during daily activities [25]. Although the reasons why only these two IFIS dimensions showed significant within-group changes remain uncertain, one possible explanation is that speed/agility and flexibility may be particularly sensitive to the biomechanical and functional adaptations that characterize pregnancy. These domains are closely related to movement efficiency, postural adjustments, and dynamic lumbopelvic control, which may be more noticeably influenced by PLBP than other dimensions of SPPF [25]. Consequently, women with PLBP may perceive greater deterioration in these dimensions, whereas other dimensions of SPPF may remain relatively unchanged.

The multivariable logistic regression model further supports the potential relevance of SPPF during pregnancy. Even after adjustment for maternal age, prepregnancy BMI, occupational posture during work activity, and PA levels, higher global IFIS scores remained independently associated with lower odds of PLBP. Interestingly, PA volume expressed as MET·min/week was not independently associated with PLBP in the adjusted model. This finding suggests that SPPF may capture clinically relevant information beyond PA volume alone, although this interpretation should be approached cautiously. From a clinical perspective, the IFIS may represent a practical and easily applicable tool for the assessment of SPPF during pregnancy. This practical value is supported by previous international evidence showing that IFIS-assessed SPPF is related to objectively measured fitness and cardiometabolic risk markers in early pregnancy [23]. Unlike objective fitness testing, the IFIS can be quickly administered in routine prenatal care without requiring specialized equipment, supervised exercise testing, or substantial economic resources. This aspect may be particularly relevant in obstetric settings where time and logistical constraints frequently limit the feasibility of objective fitness assessment.

In addition to pain itself, PLBP may substantially interfere with maternal daily functioning, negatively affecting mobility, sleep quality, occupational activities, emotional well-being, and health-related quality of life [5,40]. The absence of significant associations between IFIS scores and the exploratory obstetric and perinatal outcomes evaluated in the present investigation should be interpreted cautiously. Although women with lower SPPF showed a higher frequency of PLBP, no statistically significant relationships were observed between IFIS dimensions and occupational interruption, instrumental delivery, or fetal umbilical artery pH. These findings may reflect the relatively limited sample size available for exploratory subgroup analyses and the multifactorial nature of obstetric and perinatal outcomes. Previous investigations from the GESTAFIT Project have reported associations between better SPPF during late pregnancy and selected delivery-related outcomes, including lower oxytocin administration and more favorable birth-related parameters [30].

The present study has several strengths. First, and most importantly, this is, to the best of our knowledge, the first published study specifically evaluating the association between IFIS-assessed SPPF and PLBP in a cohort composed exclusively of physically active pregnant women who fulfilled current WHO recommendations for PA during pregnancy [15]. This unique design reduced heterogeneity related to physical inactivity, minimized the potential confounding influence of sedentary behavior, and allowed the association between SPPF and PLBP to be examined among women already meeting recommended PA levels. In addition, multiple dimensions of SPPF were evaluated using a validated instrument previously applied in pregnant populations [28]. Furthermore, the inclusion of multivariable analyses allowed adjustment for clinically relevant maternal and PA-related covariates. The study also incorporated a multidimensional assessment of PLBP and its potential clinical, functional, occupational, obstetric, and perinatal implications.

Several limitations should be acknowledged. SPPF and several PLBP variables were assessed using self-reported questionnaires, which may have introduced reporting bias. In addition, although participant recruitment and obstetric follow-up were conducted prospectively, part of the information regarding PA, IFIS scores, and PLBP characteristics was collected postpartum, thereby incorporating a retrospective component and potential recall bias into exposure assessment. To minimize this limitation, participants completed both the IPAQ and IFIS questionnaires during the first-trimester face-to-face assessment and were informed that PA and clinical variables would be reassessed after delivery, thereby facilitating familiarity with the questionnaire structure and reporting procedures. Moreover, the postpartum telephone interview was conducted within the first month after delivery, reducing the recall interval and facilitating more accurate reporting of pregnancy-related symptoms and activity patterns. Likewise, participants received the VAS in printed numerical format during recruitment and were asked to retain it for use during the postpartum telephone interview, thereby maintaining consistency in pain assessment across evaluations. Although recall bias cannot be completely excluded, previous studies have shown acceptable reproducibility and validity of maternal recall for pregnancy-related variables and PA assessment during the postpartum period [41,42]. In addition, differential recall cannot be excluded. Women who experienced more severe PLBP during pregnancy may have retrospectively rated their SPPF less favorably than women without pain, meaning that IFIS scores may have been partially influenced by participants’ pain experience rather than exclusively reflecting their SPPF during pregnancy. This potential source of information bias should therefore be considered when interpreting the observed associations. Importantly, obstetric and perinatal outcomes were obtained directly from electronic medical records and therefore were not influenced by recall bias. In addition, the IFIS evaluates SPPF rather than objectively measured physical fitness, and the findings therefore cannot be directly extrapolated to objective physiological performance parameters [27]. Finally, because the cohort was composed exclusively of physically active women with low-risk pregnancies and a high educational level, the generalizability of the findings to sedentary populations or higher-risk obstetric settings may be limited. However, the relative homogeneity of the cohort may also be considered a methodological strength, as it reduced potential confounding related to physical inactivity, major obstetric complications, and heterogeneous baseline clinical characteristics, thereby reinforcing the internal validity of the study.

5. Conclusions

Lower SPPF assessed using the IFIS was associated with PLBP in physically active pregnant women who fulfilled current WHO recommendations for PA during pregnancy. In particular, women with PLBP reported lower perceived speed/agility and flexibility during gestation, whereas higher overall IFIS scores were independently associated with lower odds of PLBP after adjustment for maternal and PA-related covariates. These findings suggest that SPPF is a clinically relevant characteristic associated with PLBP beyond PA volume alone. Given its simplicity, low cost, and ease of administration, the IFIS may be a useful tool for assessing SPPF during routine prenatal care. However, because of the retrospective nature of SPPF assessment, the present findings should not be interpreted as demonstrating a predictive or causal relationship. Its role as a screening tool for identifying women at increased risk of PLBP should be evaluated in prospective studies evaluating its predictive performance. Since PLBP most commonly emerges during the second and third trimesters, future prospective studies should evaluate whether IFIS assessment at the end of the first trimester, before the onset of the second trimester, has predictive value for the subsequent development of PLBP and could help guide targeted exercise-based preventive interventions aimed at reducing its clinical, functional, occupational, and socioeconomic burden.