J Basic Clin Physiol Pharmacol 2017; 28(3): 219–224 Mickey Scheinowitz, Ran Yanovich, Nurit Sharvit, Michal Arnon and Daniel S. Moran* Effect of cardiovascular and muscular endurance is not associated with stress fracture incidence in female military recruits: a 12-month follow up study DOI 10.1515/jbcpp-2015-0098 Received August 9, 2016; accepted January 13, 2017; previously published online February 21, 2017 Abstract Background: Stress fracture (SF) is a common injury among military recruits, especially among women, during the army basic training (ABT). The purpose of this study was to evaluate the effects of health habits and physical activity before recruitment on the fitness level and the incidence of SF during the 4-month ABT. Methods: We screened 226 female recruit volunteers (weight: 60.5 ± 10 kg; height: 163 ± 6 cm) from an inte- grated combat unit and 124 aged-matched female con- trols (weight: 57.0 ± 8.3 kg, height 162 ± 7 cm) from a non- combat unit. A self-report questionnaire on their habits pertaining to smoking, physical activity, and orthopedic injuries prior to recruitment were analyzed in relation to the incidences of SF during ABT. Results: Aerobic fitness was similar between the two groups. The overall incidence of SFs was 10.2%. Physical training prior to recruitment had no significant effect on the incidence of SF during ABT (11.7% vs. 9.6% in those who trained and did not train before recruitment, respec- tively) (Odds ratio, OR) = 1.24, p = 0.236). Nearly 42% of the female recruits smoked regularly, and the incidence of SFs among smokers was 10.5% compared with 9.9% among the non-smokers (OR = 1.07, p = 0.188). The overall incidence of SFs 12 months after recruitment was 1.78%. The use of contraceptive medication did not affect the incidence of SF: 10.0% among prior-trained vs. 6.4% in non-prior trained (p > 0.05) recruits. SFs were not corre- lated to these variables at the end of the ABT program and 16 months after recruitment. Conclusions: In the present female cohort, physical activ- ity prior to recruitment had no protective effect against SF during or after ABT. The incidence of SFs during the 12-month period after ABT was negligible. Keywords: army; basic training; contraception; female soldiers; physical activity; smoking. Introduction Stress fracture (SF) is a common injury sustained by recruits during basic training (2%–8%), with higher incidence among female recruits than males [1]. SF symptoms begin with focal pain, which worsens during activity [2]. The fractures, which are graded I–IV with bone scan or magnetic resonance imaging (MRI), most commonly occur in the tibia and feet [3, 4]. This injury indirectly causes a decrease in physical fitness due to the reduced activity caused by recruits missing training sessions and potentially being unable to serve as combat soldiers [5]. Studies have demonstrated that lower levels of physi- cal activity before army basic training (ABT) are related to musculoskeletal injuries [6]. Additionally, appropriate exercise and physical activity prior to ABT are considered to be protective measures against SFs [7, 8]. The type of exercise, duration, and intensity have been reported to have an important role in the prevention of SFs. Friedl et al. reported that resistance training is essential in this aspect. However, it requires a greater commitment of time, resources, and understanding of the science to produce strength gains that may be beneficial in preventing SFs [9]. Armstrong and colleagues showed that low impact training, such as swimming, is less protective during the *Corresponding author: Prof. Daniel S. Moran, PhD, FACSM, Ariel University, Ariel, Israel; and Heller Institute, Sheba Medical Center, Tel-Hashomer, 52621, Israel, Phone: + 972-3-5303564, Fax: + 972-3-7377002, E-mail: dmoran@sheba.health.gov.il Mickey Scheinowitz: Combat Fitness Center, Ground Forces Command, Israel; and Neufeld Cardiac Research Institute and Department of Biomedical Engineering, Tel-Aviv University, Israel Ran Yanovich: Surgeon General’s Headquarters, Israel Defense Force, and Department of Military Medicine, Hebrew University, Jerusalem, Israel; and Heller Institute, Sheba Medical Center, Israel Nurit Sharvit: Combat Fitness Center, Ground Forces Command, Israel Michal Arnon: Zinman College for Physical Education, Netanya, Israel