To examine the relationship of F-v characteristics, isometric muscle strength, jump ability and flexibility with age, performance and anthropometry, a cross-sectional study design was applied. Participants (n = 33) were divided into three age groups (<35, 35–45 and >45 years) to study the effect of age on these performance parameters. Also, differences among three even performance groups, based on the best race time (fast 3:53 ± 0:19 h:min, <4:15 h:min, n = 11; medium 4:30 ± 0:07 h:min, 4:15–4:45 h:min, n = 11; slow 5:14 ± 0:30 h:min, >4:45 h:min, n = 11), were examined. The best race time was considered instead of the most recent race time as the latter could be influenced by non-performance conditions, e.g., injury. The relationship of physical fitness (sit-and-reach test – SAR, squat jump – SJ, CMJ, isometric strength, and F-v test) with anthropometric characteristics (body mass, body mass index – BMI, body fat percentage – BF, total thigh muscle cross-sectional area – CSA, and fat-free mass – FFM) was examined using correlations.

Thirty-three female recreational marathon runners (age 40.0 ± 8.9 years, height 162 ± 6 cm, body mass 57.7 ± 7.4 kg, BMI 21.8 ± 2.1 kg.m⁻² and personal record 4:34 ± 0:39 h:min, completed marathons in the past 3.3 ± 3.6) mostly from the area of Athens volunteered to participate in this study, which had been advertised through popular websites for endurance runners. The participants reported sport experience 5.6 ± 4.6 years and were practicing endurance training for 4.1 ± 1.5 days weekly with each training session corresponding to 9.3 ± 2.8 km or 1.6 ± 0.5 h. During September and October 2017, the participants visited the laboratory where they were examined for anthropometric characteristics and performed a F-v test, isometric muscle strength, jump ability and flexibility. This study was approved by the local Institutional Review Board (Exercise Physiology Laboratory, Nikaia). The study was conducted in accordance with the Declaration of Helsinki. All participants gave written informed consent after having been provided detailed information about the risks and benefits of the research.

Statistical analyses were performed using IBM SPSS v.20.0 (SPSS, Chicago, IL, United States) and GraphPad Prism v. 7.0 (GraphPad Software, San Diego, CA, United States). Normality was examined using Kolmogorov-Smirnov test and visual inspection of normal Q-Q plots. Data were expressed as mean and standard deviation (SD). One-way repeated measures analysis of variance (ANOVA) and a subsequent Bonferroni post hoc test (if there were differences among groups) were used to examine the differences among age and performance groups, separately. To interpret effect size (ES) for statistical differences in the ANOVA, partial eta square classified as small (0.010 < η_p²≤ 0.059), medium (0.059 < η_p²≤ 0.138), and large (η_p² > 0.138) was used (Cohen, 1988). The relationship of flexibility, isometric muscle strength, jumping ability and F-v characteristics with age, performance and anthropometry was examined using Pearson’s product moment correlation coefficient (r). Magnitude of correlation coefficients was considered as trivial if r < 0.10, small if 0.10 ≤r < 0.30, moderate if 0.30 ≤r < 0.50, large if 0.50 ≤r < 0.70, very large if 0.70 ≤r < 0.90, nearly perfect if r ≥ 0.90, and perfect if r = 1.00 (Batterham and Hopkins, 2006). The level of significance was set at α = 0.05.

The anthropometric characteristics of participants, in total and by age group, can be seen in Table 1. In the F-v test, v₀ of all participants was 167 ± 15 rpm (ranging from 132 to 195 rpm), F₀ 120 ± 20N (93–179 N), Pmax 507 ± 85W (340–704 W), rPmax 8.83 ± 1.17 W.kg⁻¹ (6.0–11.1 W.kg⁻¹) and v₀.F₀⁻¹ 1.43 ± 0.28 rpm.N⁻¹ (0.87–1.93 rpm.N⁻¹). With regards to neuromuscular fitness, SAR was 25.8 ± 8.3 cm (8.0–37.5 cm), SJ 17.7 ± 3.4 cm (10.3–25.2 cm) and CMJ 18.6 ± 3.7 cm (11.2–26.1 cm). In isometric muscle strength, right handgrip was 29.7 ± 4.5 kg (20.7–41.6 kg), left handgrip 29.7 ± 4.0 kg (23.4–39.7 kg), back 82.5 ± 16.2 kg (40.0–114.0 kg), back-and-leg 94.9 ± 19.0 kg (48.5–150.0 kg), sum 236.9 ± 40.1 kg (134.2–339.3 kg) and 4.12 ± 0.56 kg.kg⁻¹ (2.90–5.23 kg.kg⁻¹).

A large main effect of age on SJ (p = 0.002, η_p² = 0.361) and CMJ (p = 0.001, η_p² = 0.384) was observed with higher values in the <35 age group than in the 35–45 and >45 age group, whereas no difference was shown in SAR (p = 0.912, η_p² = 0.006) (Figure 1). No difference was found in isometric muscle strength (Figure 2). With regards to F-v characteristics, a large main effect was observed on v₀ (p = 0.034, η_p² = 0.208), F₀ (p = 0.004, η_p² = 0.323) with higher score in 35–45 than <35 and >45 age group, Pmax (p = 0.037, η_p² = 0.203) with higher score in 35–45 than >45 age group, rPmax (p < 0.001, η_p² = 0.468) with higher score in <35 and 35–45 than >45 age group and v₀/F₀ (p = 0.002, η_p² = 0.354) with higher score in <35 than 35–45 age group (Figure 3).

Anthropometric characteristics and physical fitness by performance level can be seen in Table 2. A large main effect of performance on flexibility was observed (p = 0.039, η_p² = 0.201) with higher score (+8.3 cm) in the slowest than in the average performance group.

SJ and the sum of isometric strength tests (in relative values) correlated inversely moderately with BF (Table 3). All the other indices of isometric strength correlated largely with body mass, FFM and CSA. It should be highlighted that the magnitude of these correlations with FFM was larger than body mass. Vo and rPmax did not correlate with any anthropometric characteristic, whereas F0 and Pmax correlated largely with body mass and FFM.

CMJ was in similar levels as sex- and age-matched general population (Edwen et al., 2014). Participants had lower CMJ and F-v characteristics than volleyball players (Nikolaidis, 2013) indicating that female marathon runners characterized by physiological range of muscle strength and power. This observation was in agreement with research in male runners, where relatively low scores of anaerobic power were shown in marathon runners compared to shorter distances’ runners (Vuorimaa, 1996; Legaz-Arrese et al., 2011). For instance, CMJ in male marathon runners was ∼13 cm and 24 cm lower than middle-distance runners and sprinters, respectively (Vuorimaa, 1996). All measures of isometric muscle strength (right and left handgrip, back, leg, total, and relative) were classified as average compared to general population (Heyward and Gibson, 2014).

The older age group had lower jumping ability, F₀, Pmax and rPmax than their younger counterparts, suggesting a decline of these physical fitness components with aging and indicating that probably the chronic endurance exercise does not prevent from loss in muscle strength and power. It should be highlighted that the participants had sport experience in endurance running for 5.6 years. These findings confirmed previous studies in male participants which showed a decline of anaerobic power with aging (Chamari et al., 1995; Bonnefoy et al., 1998). For instance, in a comparison between young (25 years) and master athletes (65 years) matched for weight, height and training, P_max was ∼43%, F₀ 30% and v₀ 15% lower in the older athletes (Chamari et al., 1995). A study of young (23 years) and elder male participants (71 years) showed a decline of rP_max by 8% per decade and of velocity by 4%, and a moderate inverse relationship between rP_max and age (r = -0.33) (Bonnefoy et al., 1998).

Among all anthropometric characteristics and physical fitness components examined in the present study, flexibility was the only one observed to differ among performance groups with the slowest one presenting the better score in SAR than the average group. This observation might be due to that running economy (which is related with performance) is inversely correlated with sit-and-reach test score (Jones, 2002; Trehearn and Buresh, 2009). An increased storage and return of elastic energy in stiffer musculotendinous structures might reduce the aerobic demand of submaximal running (Drew et al., 2011). In addition, no difference was shown among performance groups with regards to muscle strength and power. This finding was in agreement with a previous research showing that fast marathon runners were not characterized by high anaerobic power (Vuorimaa, 1996; Legaz-Arrese et al., 2011).

Most indices of muscle strength and power correlated with both body mass, FFM and CSA, which might explain why female marathon runners are not characterized by high levels of muscle strength and power as their body dimensions are relatively small compared to other sports. An excess of FFM, even if this is “active mass,” is a load that marathon runners need to carry with them; thus, their profile consists of small anthropometric characteristics and corresponding moderate levels of muscle strength and power. Although an increased Pmax might improved the cost of running (Giovanelli et al., 2017), its association with increased FFM would lead to slower race time.

A limitation of the present study was the specificity of protocols that assessed the various physical fitness components as caution would be needed to compare their findings with studies using other protocols. For instance, F-v test and WAnT reflect different aspects of anaerobic power and capacity and their findings should not be used interchangeably (Jaafar et al., 2016). Strength of this study was its novelty since it was the first to examine flexibility, isometric muscle strength, two jump tests (SJ and CMJ) and F-v characteristics of female marathon runners and the findings could be used as norms and references for future studies. Considering the gap in the existing literature about these physical fitness components in female marathon runners, the findings add new information. The present study confirmed on female runners the findings of previous studies on male runners showing that flexibility, muscle strength and power were not related to performance in marathon runners. On the other hand, flexibility and muscle strength are components of the health-related physical fitness, and in this context, they should be regularly monitored in addition to sport-related physical fitness components, such as aerobic capacity (maximal oxygen uptake, anaerobic threshold, and running economy). In view of the increased female participation in marathon races during the last decades (Lepers and Cattagni, 2012), the findings were of great practical value for strength and conditioning coaches in the context of training and testing of their runners. Surprisingly, although an optimal level of flexibility and muscle strength is important for health, these fitness components have been rarely studied in male marathon runners (Maud et al., 1981). Thus, the present study filled a gap in the existing literature as it was the first study – to the best of our knowledge – to provide data on F-v characteristics and the abovementioned health-related physical fitness components in female marathon runners.