Power, Endurance, and Body Composition Changes Over a Collegiate Career in National Collegiate Athletic Association Division I Women Soccer Athletes

Abstract

McFadden, BA, Bozzini, BN, Cintineo, HP, Hills, SP, Walker, AJ, Chandler, AJ, Sanders, DJ, Russell, M, and Arent, SM. Power, endurance, and body composition changes over a collegiate career in National Collegiate Athletic Association Division I women soccer athletes. J Strength Cond Res 37(7): 1428–1433, 2023—The purpose of this study was to determine longitudinal changes in fitness and body composition throughout athletes' 4-year collegiate soccer careers. Performance testing occurred before preseason during freshman, sophomore, junior, and senior year in 17 female Division I soccer players. Body composition was assessed through air-displacement plethysmography to determine percent body fat (%BF), fat-free mass (FFM), and body mass (BM). Maximal countermovement vertical jump height was assessed through contact mat using arm swing (CMJ_AS) and hands-on-hips (CMJ_HOH) methods to calculate power (CMJ_watts/_HOHwatts). Aerobic capacity (V̇o₂max) and ventilatory threshold (VT) were assessed by indirect calorimetry during a maximal graded exercise test on a treadmill. Linear mixed models were used to assess changes across academic years (p < 0.05). No changes occurred in %BF, BM, V̇o₂max, VT, CMJ_AS, or CMJ_watts. A time main effect was seen for FFM (p = 0.01) with increases from freshman to senior (p = 0.02). Time main effects were observed for CMJ_HOH (p < 0.001) and CMJ_HOHwatts (p < 0.001) with increases from freshman to junior (CMJ_HOH,p = 0.001; CMJ_HOHwatts, p = 0.02) and senior (CMJ_HOH, p < 0.001; CMJ_HOHwatts, p = 0.003) as well as sophomore to senior (CMJ_HOH, p < 0.001; CMJ_HOHwatts, p = 0.02). Countermovement vertical jump with hands on hips also increased from sophomore to junior (p = 0.005). The lower FFM and power capabilities as freshmen compared with upperclassman indicate a potential limited readiness. Coaches and training staff should account for these developmental differences when entering the preseason. Adequate conditioning programs before starting a collegiate program may help build a fitness foundation and prepare freshmen athletes to compete at the same level as their upperclassmen counterparts.

Introduction

National Collegiate Athletic Association (NCAA) teams are faced with a unique set of challenges to athlete development and management because players are limited in their time spent on the team. Collegiate athletes have 4 seasons of eligibility to compete in their respective sport, giving coaches and training staff a narrow period to optimize athlete performance before they complete their collegiate careers. A compounding challenge for fall sport coaches and training staff is the limited access allowed to the athletes before the start of their season each year. The NCAA rules and regulations stipulate that college athletes and coaching staff cannot engage in supervised athletic activities outside their playing season, which is defined as the period between the first official practice session and either the last practice session or date of competition, whichever occurs later (¹⁹). These rules present a unique set of challenges to fall collegiate sport teams because the time coaches are able to spend integrating incoming freshmen into the team is limited, leading up to the competitive season.

The NCAA soccer season starts in the beginning of August with a ∼2-week preseason (21 unit) that often consists of multiple practices per day (¹⁹). This is followed by a 12-week competitive season consisting of ∼20 matches followed by tournament play (¹⁹). Entering the preseason period in peak physical condition is essential because this 2-week period is associated with the highest workloads seen throughout the year and has been shown to result in several physiological and psychological perturbations, which seem to be further exacerbated by the cumulative effects of the season (¹⁷). Therefore, coaches expect individual athletes to train on their own in the offseason summer months to adequately prepare for the demands of the season. A major constraint to a team's offseason fitness plan is incoming freshmen's knowledge of what is required for conditioning. Freshmen (∼18 years old) are expected to compete alongside their senior teammates (∼22 years old); however, unlike seniors, freshmen are less familiar with the training demands associated with collegiate sports. Soccer requires both high levels of aerobic fitness and muscular power for on-field success (^26,29); yet, freshmen often lack sufficient resistance training knowledge and experience before entering college. Thus, freshmen often demonstrate disparities in strength and power capabilities, putting them at greater risk of injury, compared with collegiate upperclassmen (^{9,12,18,21,25}).

Periodic testing of fitness attributes is crucial to aid in maximizing team success. As soccer is a power-endurance sport, it is important to track changes in these metrics throughout an athlete's career. Changes in performance may be a result of baseline fitness, competitive level of the athlete (starters vs. nonstarters), offseason activity, and training strategies (¹¹). Body composition also plays a critical role in sport success because significant correlations between body composition variables and physical performance have been found (²⁴). Greater fat mass has been related to slower sprint times and lower aerobic capacity, whereas greater percent body fat (%BF) has been correlated with lower vertical jump and cardiorespiratory endurance in male collegiate soccer players (²⁴). As such, longitudinal testing may help to ensure adequate development of the physical and performance qualities that are needed for sport success.

Although performance data are important to team success, limited research exists on normative values in female collegiate players. Furthermore, most available data rely on field-based testing measurements rather than gold-standard laboratory-based testing procedures (^13,28). Research assessing female collegiate athlete performance variables using gold-standard testing metrics is warranted. This information can then be used to guide performance goals for coaches and training staff at both the collegiate level as well as the high school level, where players are aiming to transition and secure a role on an NCAA team. Moreover, research aimed at understanding the longitudinal changes in fitness variables throughout an athlete's collegiate career may help to elucidate the differences that occur across academic years. The purpose of this longitudinal study was to determine fitness and body composition changes over a 4-year period in NCAA Division I women soccer athletes. We hypothesized that these fitness parameters would improve as players progressed from their freshman to senior year.

Methods

Experimental Approach to the Problem

Maximal performance testing and body composition data were collected over a 7-year period (2013–2019) in women collegiate soccer athletes. Testing sessions occurred immediately before preseason (in late July) each academic year. Academic years were defined as freshman, sophomore, junior, and senior year, respectively.

Subjects

Fitness variables in women collegiate soccer players on a highly ranked NCAA Division I program were assessed as part of an integrative sport science program. A total of 17 players (age = 19 ±1 year) who participated in all 4 testing sessions over their respective 4-year academic eligibility period were included in the analysis. Analyses for each variable include athletes with complete testing data (Table 1). All athletes received clearance by the University Sports Medicine staff before all testing sessions. This research was approved, and written informed consent was waived by the Rutgers University Institutional Review Board for the Protection of Human Subjects (IRB#16-050M). All procedures performed were in accordance with the 1964 Declaration of Helsinki and its later amendments or comparable ethical standard.

Table 1 - Body composition and performance changes across academic years.^*†

Academic years	N	Freshman	Sophomore	Junior	Senior	Time main effect (P value)
BF (%)	11	19.7 ± 3.9	20.3 ± 3.9	18.8 ± 5.7	18.3 ± 5.5	0.40
FFM (kg)	11	53.4 ± 4.8	53.9 ± 4.8	54.6 ± 4.8	55.0 ± 3.8‡	0.01
Body mass (kg)	11	66.4 ± 4.4	67.6 ± 5.4	67.4 ± 5.6	67.5 ± 5.2	0.70
CMJAS (cm)	17	53.8 ± 6.8	53.8 ± 7.2	55.7 ± 5.6	55.2 ± 5.8	0.27
CMJAS (watts)	17	4,123 ± 515	4,179 ± 559	4,287 ± 449	4,256 ± 505	0.17
CMJHOH (cm)	9	45.2 ± 6.0	45.8 ± 3.6	49.8 ± 4.8‡§	51.0 ± 4.1‡§	<0.001
CMJHOH (watts)	9	3,688 ± 419	3,761 ± 364	3,990 ± 426‡	4,061 ± 321‡§	0.001
V̇O2max (ml·kg−1·min−1)	16	50.1 ± 2.7	50.0 ± 5.6	48.5 ± 3.6	49.8 ± 3.4	0.37
VT (%V̇O2max)	16	80 ± 3	80 ± 5	80 ± 5	79 ± 4	0.79

^*VT = ventilatory threshold; CMJ_AS = countermovement vertical jump with arm swing; CMJ_HOH = countermovement vertical jump with hands on hips; BF = percent body fat; FFM = fat-free mass.

^†Results are presented as mean and SD.

^‡Significant differences from freshman (p < 0.05).

^§Significant differences from sophomore (p < 0.05).

Procedures

Body Composition

Body composition was assessed using air-displacement plethysmography (BOD POD, COSMED, Concord, CA). Athletes arrived in a normally hydrated state, ≥2 hours fasted, and having refrained from exercise and caffeine ∼24 hours earlier. Athletes dressed according to manufacturer guidelines for all tests. Body mass (BM) was determined using a calibrated scale, and %BF and fat-free mass (FFM) were calculated using the Brozek formula (^1,3).

Countermovement Vertical Jump

After a ∼7-minute dynamic warm-up, athletes completed vertical jump testing through a digital contact mat (Just Jump, Probotics, Huntsville, AL) to determine maximal vertical jump height (²⁰). Athletes were given 2 attempts to achieve maximal jump height using a countermovement vertical jump (CMJ) with arm swing (CMJ_AS) and CMJ with hands on hips (CMJ_HOH). Countermovement vertical jump with hands on hips was added to the testing battery during the 2016 season because it has been suggested to be a more sensitive metrics to evaluate lower-body force production (²), and thus, only 9 athletes completed this part of the testing procedures. Muscular power was calculated using the Sayers formula for all jumps (CMJ_watts and CMJ_HOHwatts) (²²).

Aerobic Capacity

Athletes performed a graded exercise test on a treadmill to measure maximal aerobic capacity (V̇O_2max) through direct gas exchange using an indirect calorimeter (Quark CPET, COSMED, and Parvo Medics, Sandy, UT). Throughout the test, heart rate (HR) was continuously monitored using a chest strap HR monitor (Polar Electro Co., Woodbury, NY). At least 3 of the following criteria were met verifying attainment of V̇O_2max. The criteria were as follows: a leveling off or plateauing of V̇O₂ with an increase in workload, attainment of age predicted maximal HR ±10 bpm (HR_max), a respiratory exchange ratio ≥1.10, and an rating of perceived exertion ≥18 (²⁷). Subject's ventilatory threshold (VT) was calculated after the completion of each test as the point where ventilation increased nonlinearly with V̇O₂.

Statistical Analyses

Linear mixed models were used to assess changes in physical performance variables across different academic years to account for the unbalanced nature of data arising through repeated measurements of the same individuals. Separate models were constructed for each dependent variable, whereby individual “player ID” was modeled as a random intercept throughout. As per the research questions of interest, “academic year” (“freshman,” “sophomore,” “junior,” and “senior”) was specified as categorical fixed effects. Visual checks were used to confirm the assumptions of normality and linearity. Pairwise comparisons were made using a Bonferroni-adjusted post hoc test to assess differences between each level of any given fixed effect. The t statistics from the model comparisons were converted into standardized effect sizes (d), which were interpreted as trivial (<0.20), small (0.20–0.59), moderate (0.60–1.19), or large (1.20–1.99) (^6,8,10). Descriptive data by academic year are presented as mean and SD. Analyses were conducted in RStudio (v R-3.6.1.) using the lme4, emmeans, and effsize packages.

Results

Body composition and performance metrics across academic years are presented in Table 1. No significant changes were seen in %BF, BM, V̇O_2max, VT, CMJ_AS, or CMJas watts across academic years (p > 0.05). A time main effect was seen for FFM (p = 0.01). Pairwise comparisons revealed the greatest change occurred from freshman to senior year (Δ = 1.6 kg; d = 0.33; p = 0.02). A significant time main effect was observed for CMJ_HOH (<0.001) and CMJ_HOHwatts (p = 0.001). Pairwise comparisons revealed a significant increase in CMJ_HOH occurred from freshman to junior (Δ = 4.6 cm, d = 0.77, p = 0.001) and senior year (Δ = 5.8 cm, d = 0.97, p < 0.001), as well as sophomore to junior (Δ = 3.8 cm, d = 1.11, p = 0.005) and senior year (Δ = 5.2 cm, d = 1.44, p < 0.001). Pairwise comparisons also revealed a significant increase in CMJ_HOHwatts occurred from freshman to junior (Δ = 303 W, d = 0.72, p = 0.02) and senior year (Δ = 373 W, d = 0.89, p = 0.003), as well as sophomore to senior year (Δ = 300 W, d = 0.82, p = 0.02) (Figures 1–3).

Figure 1.: Body composition changes over an academic career in female collegiate soccer athletes. (A) Body fat changes; (B) fat free mass changes. Lines represent individual athlete changes over 4 years. Diamonds represent mean values for each academic year. FFM = fat-free mass.

Figure 2.: Endurance changes over an academic career in female collegiate soccer athletes. A) Vo₂max changes; (B) ventilatory threshold changes. Lines represent individual athlete changes over 4 years. Diamonds represent mean values for each academic year. Vo₂max = maximal aerobic capacity.

Figure 3.: Power changes over an academic career in female collegiate soccer athletes. Lines represent individual athlete changes over 4 years. Diamonds represent mean values for each academic year. A) Countermovement vertical jump using arm swing changes; (B) countermovement vertical jump using arm swing power output changes; (C) countermovement vertical jump using hands on hips changes; (D) countermovement vertical jump using hands on hips power output changes. CMJ = countermovement vertical jump with arm swing; CMJHOH = countermovement vertical jump with hands on hips.

Discussion

Although endurance levels (aerobic capacity and VT), CMJ_AS, and %BF were maintained over the 4 years, athletes' lower extremity muscular power and FFM significantly improved. Athletes exhibited the lowest FFM, CMJ_HOH, and power outputs as freshmen, indicating a significant development in these areas throughout their collegiate careers. Overall, these findings indicate that incoming collegiate freshmen do not possess the same physical and performance attributes as their older, seasoned collegiate teammates, especially in terms of muscular power capabilities.

In the current study, aerobic capacity and VT did not improve over the 4 years. The homogeneity in team aerobic performance, as well as the relatively high values seen across academic years, may be reflective of the high-level athlete and the type of training they are accustomed to pursuing in the offseason. It is speculated that without access to team strength coaches and facilities over the summer months, athletes may be more apt to choose endurance-based exercise and soccer-specific training programs to maintain fitness, leading to the high aerobic capacity values seen before preseason.

Given the often limited exposure to strength training at the high school level, the lower FFM observed freshman year is not surprising. In fact, the lower FFM observed at freshmen year in this study is similar to those previously found in men's collegiate basketball (⁴). Male basketball players experienced an increase in FFM from freshman to sophomore year with no change from sophomore to junior year (⁴). In addition, previous cross-sectional data detailing performance characteristics across different academic years in female collegiate soccer players also found freshmen had significantly lower maximal power capabilities compared with upperclassmen, along with lower maximal aerobic capacity (¹⁴). It is important to note that although CMJ_AS did not change significantly over the 4 years, this may be a result of a lack of sensitivity of this measure when tested in soccer athletes whose sport does not require the use of arm swing motion for jump proficiency (⁷). In addition, despite lack of significant changes in this metric over the 4-year period, the lowest values were still apparent during freshman year.

Overall, coaches and training staff should recognize the potential limited readiness of freshmen athletes and account for these developmental differences when entering the season. This may aid proper periodization strategies and help to reduce the risk of injury. In fact, studies in collegiate athletes across sports have reported freshmen were at a higher risk of stress fracture occurrence, which may be caused by the increase in training demands transitioning from the high school to collegiate level (⁵). In addition, because power and body composition differences in freshman seem to be prevalent across multiple sports, coaches and training staff can use this information to tailor training in an effort to address these concerns. Because of the limited access to their team, it becomes crucial for coaches and training staff of collegiate fall sports to maximize their time spent with the athletes throughout the year to achieve long-term team success. This should include targeted strength and power training, especially for freshman female soccer players. Moreover, for high school athletes, there seems to be a need for improved strength and conditioning programs aimed at increasing FFM and power capabilities beginning before sport participation at the collegiate level. Further research is warranted regarding maturation and performance development in youth athletes looking to transition to a collegiate program.

An acknowledged limitation of the current study is lack of training workload information to provide context to the performance changes that were seen over the 4-year period. Other studies have shown increased training load improves aerobic fitness (²³), but that these training loads may also have a negative effect on sprint and CMJ performance (^15,16). Given the design of a collegiate soccer program, monitoring individual training workloads throughout the years was not possible, particularly during NCAA mandated unsupervised periods. Future research is warranted to assess total training demands to help explain the changes in performance and body composition throughout the season. Further research may benefit from this information to help determine optimal loading prescriptions in an effort to mitigate performance decrements in this population. Despite these limitations, this study has many unique strengths. The within-subject design of this study helps to elucidate the developmental changes that occur over time in women soccer athletes. To the best of authors' knowledge, this is the first study to determine longitudinal changes in fitness variables using gold-standard testing techniques throughout an entire collegiate soccer career.

Practical Applications

This study highlights the importance of monitoring performance across the entirety of an athlete's career. Periodic testing may help to ensure adequate development of the physical and performance qualities that are needed for sport success at all levels of play. Performance testing before the start of an athlete's collegiate career may be especially crucial because it allows coaches and training staff to identify athlete's readiness and immediately implement targeted interventions to address any deficits. This individualized approach to team monitoring becomes essential because not all athletes may adapt to the imposed training demands in a similar manner. In addition, adequate conditioning programs before entering a collegiate program may help to build a proper fitness foundation and prepare incoming freshmen athletes to compete at the same level as their upperclassmen counterparts. These findings can guide performance goals for soccer coaches and training staff at both the collegiate and high school levels to better prepare freshmen to compete on the collegiate stage. For women soccer players, these programs should emphasize power development because these characteristics were the most improved throughout the 4-year collegiate period.