The Addition of Sprint Interval Training to Field Lacrosse Training Increases Rate of Torque Development and Contractile Impulse in Female High School Field Lacrosse Players

eld lacrosse requires sudden directional changes and rapid acceleration/deceleration. The capacity to perform these skills is dependent on explosive muscle force production. Limited research exists on the potential of sprint interval training (SIT) to impact explosive muscle force production in eld lacrosse players. The purpose of this study is to examine SIT, concurrent to eld-lacrosse-speci c training, on the rate of torque development (RTD), contractile impulse, and muscle function in female high school eld lacrosse players (n = 12; 16 1 yrs.). SIT was performed three times per week, concurrent to eld-lacrosse-speci c training, for 12 weeks. Right lower-limb muscle performance was assessed pre-, mid-, and post-SIT training via isometric and isokinetic concentric knee extensor contractions. Outcomes included RTD (Nm s 1 ), contractile impulse (Nm s), and peak torque (Nm). RTD for the rst 50 ms of contraction improved by 42% by midseason and

three times per week, concurrent to eld-lacrosse-speci c training, for 12 weeks. Right lower-limb muscle performance was assessed pre-, mid-, and post-SIT training via isometric and isokinetic concentric knee extensor contractions. Outcomes included RTD (Nm s 1 ), contractile impulse (Nm s), and peak torque (Nm). RTD for the rst 50 ms of contraction improved by 42% by midseason and remained elevated at postseason (p= 0.004, effect size (ES) = 577.3 to 66.5). Contractile impulse demonstrated a training effect across 0–50 ms (42%,p= 0.004, ES = 1.4 to 0.4), 0–100 ms (33%,p= 0.018, ES = 3.1 to 0.9), and 0–200 ms (22%,p= 0.031, ES = 7.8 to 1.6). Isometric (0 rad s 1 ) and concentric (3.1 rad s 1 ) strength increased by 20% (p= 0.002, ES = 60.8 to 20.8) and 9% (p= 0.038, ES = 18.2 to 0.0) from SIT and eld-lacrosse-speci c training, respectively (p< 0.05). SIT, concurrent to eld-lacrosse- speci c training, enhanced lower-limb skeletal muscle performance, which may enable greater sport-speci c gains. Keywords: high-intensity interval training; skeletal muscle function; isometric strength; isokinetic concentric strength 1. Introduction Women's eld lacrosse is a global sport with a total of 29 nations competing at the highest level [1]. Its popularity within the United States of America continues to grow with 96,762 female high school participants and 3028 high schools, competing in women's eld lacrosse in 2022 [2]. With the popularity of women's eld lacrosse growing at the club, high school, university, and national levels, it is important for athletes, coaches, and healthcare professionals, such as athletic trainers and physical therapists, to explore and develop appropriate training strategies to optimize performance in women's eld lacrosse. As a sport, eld lacrosse demands a high degree of coordination, agility, and speed from its players, as performance includes rapid changes in direction, continuous activity, transitions between acceleration and deceleration, and multiple bouts of intermittent high- intensity sprints [3]. Studies investigating sprint-related workloads during a college eld lacrosse game for female players found that they can cover a distance of 656 m at speeds J. Funct. Morphol. Kinesiol.2023,8, 89.

and speed from its players, as performance includes rapid changes in direction, continuous activity, transitions between acceleration and deceleration, and multiple bouts of intermittent high- intensity sprints [3]. Studies investigating sprint-related workloads during a college eld lacrosse game for female players found that they can cover a distance of 656 m at speeds J. Funct. Morphol. Kinesiol.2023,8, 89.

J. Funct. Morphol. Kinesiol.2023,8, 89 2 of 14 greater than 15 km h 1 , reach maximum speeds ranging from 24.1 to 26.2 km h 1 , and experience high-intensity acceleration counts between 51 and 177 during a game [4,5]. The capacity to perform these skills during competition and/or training requires su- perior lower-limb skeletal muscle strength and an enhanced ability to generate force rapidly [6,7]. Sprint exercises are an extensively used training approaches throughout Europe, the United States, Australia, and many other countries [8] due to their association with greater sports performance [9,10]. They are employed by training and coaching staff to increase skeletal muscle function and improve high-speed movements [11]. Research demonstrated sprint training signi cantly improves skeletal muscle power output; max- imal 10, 20, and 30 m sprint speed; and linear acceleration [6,9,10,12]. Taylor et al. [6] proposed that improvements in skeletal muscle power and sprint speed likely resulted from enhancements in contractile properties and further adaptations to the lower-limb extensor muscles via the repeated production of rapid high-force contractions associated with sprint training [10,13–15]. Rapid force/torque production is an important characteristic of human skeletal muscle function and is vital to successful sports performance [16,17]. A high rate of force/torque development is a signi cant contributor to the performance of rapid and forceful move- ments [17]. Rapid and forceful movements require athletes to contract their skeletal muscles over short time intervals, which may not permit the generation of maximal skeletal muscle force to be attained [18,19]. The rate of force/torque development is a common parameter used to measure skeletal muscles' capacity to generate force/torque and is obtained from the force– or torque–time curves during explosive/rapid isometric contractions [16,17]. Research has indicated that rapid force/torque generation may be a more sensitive determi- nant of acute and chronic adaptations to the neuromuscular system than maximal voluntary contractile force following strength training [16,20–22]. Research to date has shown signi - cant improvements in the rate of force/torque development following various modes of resistance training [23]. Traditional machine-based and free-weight resistance training pro- grams, in addition to explosive dynamic and static

a more sensitive determi- nant of acute and chronic adaptations to the neuromuscular system than maximal voluntary contractile force following strength training [16,20–22]. Research to date has shown signi - cant improvements in the rate of force/torque development following various modes of resistance training [23]. Traditional machine-based and free-weight resistance training pro- grams, in addition to explosive dynamic and static (isometric) resistance training programs, signi cantly enhance the rate of force/torque development [24–26]. To date, no study to our knowledge has examined the effect of sprint interval training (SIT) on skeletal muscle function, as assessed by the rate of torque development, contractile impulse, and skeletal muscle strength in young female eld lacrosse players. If effective as a means of enhancing skeletal muscle function, and in combination with its known bene ts in aerobic tness, SIT may be a valuable and ef cient training strategy for the sport of eld lacrosse. Further, SIT may enable athletes to realize optimal gains in more than one facet of eld lacrosse performance during a single training session [27,28]. Thus, the current study aimed to determine the effects of SIT, in combination with eld lacrosse-speci c training on lower-limb rate of torque development, contractile impulse, and skeletal muscle function in female high school eld lacrosse players. It is hypothesized SIT plus eld-lacrosse-speci c conditioning would improve rate of torque development, contractile impulse, and skeletal muscle strength. To test this hypothesis, we exposed participants to SIT three times per week for 12 weeks and assessed their lower-limb skeletal muscle performance via isokinetic concentric dynamometry. 2. Materials and Methods 2.1. Participants and Study Design Fourteen healthy female high school eld lacrosse players (age: 16.0 0.9 yrs., height: 161.2 5.3 cm, mass: 61.9 11.2 kg, body mass index: 23.9 4.5 kg/cm 2 , percent body fat: 27.5 6.5) volunteered to participate. Inclusion required the participants to be active members of the female varsity high school eld lacrosse team. Players were informed of the purpose of the research study and were instructed that declining to participate would not affect their selection to the team or in uence their playing

23.9 4.5 kg/cm 2 , percent body fat: 27.5 6.5) volunteered to participate. Inclusion required the participants to be active members of the female varsity high school eld lacrosse team. Players were informed of the purpose of the research study and were instructed that declining to participate would not affect their selection to the team or in uence their playing time. To control for physical maturation, each subject completed the Self-Administered Pubertal Stage Survey, which is consistent with physician-conducted pubertal staging and provides a maturation

J. Funct. Morphol. Kinesiol.2023,8, 89 3 of 14 score similar to those of the Tanner scale [29,30]. Participants were free of any lower-limb musculoskeletal or neuromuscular limitations and had not incurred a severe lower-limb or hip fracture within the past three years. Informed written parental consent and participant assent were obtained prior to participation, and all experimental procedures were approved by the Human Subjects Research and Institutional Review Board. Participants served as their own control, as no control group (i.e., eld-lacrosse-speci c conditioning only) was employed in the current study. As identi ed by Chapman et al. [31] it would be unethical to not allow all players to participate fully in every training session across the preseason and competitive season. Participants were familiarized with all testing procedures prior to data collection. Further, all participants completed three testing sessions: preseason, midseason, and postseason. Isometric and isokinetic concentric knee extensor testing was performed on the participant's dominant lower limb. The study timeline spanned 15 weeks and included both the preseason (three weeks) and competitive season (nine weeks), with the participants scheduled to take part in 33 training sessions. Two participants were unable to complete the study due to injury and illness. Therefore, an overall total of 12 female high school eld lacrosse players completed the study. 2.2. Procedures 2.2.1. Isometric and Isokinetic Testing The Biodex Quick Set System 3 dynamometer (Biodex Medical Systems, Shirley, NY, USA) was used for all isometric and isokinetic strength testing with a sampling frequency of 100 Hz [32–34]. All strength tests were analyzed using the Biodex Advantage Software, version 3.2. The Biodex was calibrated in accordance with the manufacturer's speci cations before the start of each testing session. Each participant was seated in an upright position in the Biodex chair with a seat back angle of ~85 . To limit extraneous body movements all participants were stabilized via two shoulder straps that crossed the participant's chest, a waist strap, and a thigh strap. The lateral femoral epicondyle was aligned with the center of the dynamometer shaft to establish the axis of rotation around the knee joint. The

the Biodex chair with a seat back angle of ~85 . To limit extraneous body movements all participants were stabilized via two shoulder straps that crossed the participant's chest, a waist strap, and a thigh strap. The lateral femoral epicondyle was aligned with the center of the dynamometer shaft to establish the axis of rotation around the knee joint. The participant's range of motion was then determined by having them completely extend (0 ) their lower limb and slowly return it to a comfortable position slightly past 90 exion. To negate the in uence of gravity, the lower limb was weighted according to the manufacturer's speci cations. The participant's lower limb was fully extended to maximize the gravitational effect, at which point the Biodex Advantage software established gravity correction. This correction was then applied to all strength measurements. Before the start of isometric and isokinetic concentric knee extensor testing, a ve- minute warm-up was performed on a stationary cycle ergometer at ~50 rpm against one kilopond of resistance. The sequence of testing was standardized for all participants with isometric torque at 0 rad s 1 (5 s hold, knee angle ~90 ) and assessed rst, followed by isokinetic concentric torque, which was randomized for angular velocity (1.57 rad s 1 and 3.14 rad s 1 ) across all participants. The participants performed six maximal knee extensor contractions at all angular velocities and were instructed to kick as fast and as hard as possible [18,35,36], and a ten-second rest was given between each contraction, during which time the lower limb was passively returned to the starting knee angle of ~95 . A 60 s rest period was given between each isometric contraction to compensate for the longer contraction duration (5 s) [37,38]. A two-minute rest period was given between each angular velocity. Outcome measures included peak isometric and isokinetic knee extensor concentric torque (Nm) with the highest value of the six maximal repetitions performed used for all data and statistical analysis. 2.2.2. Data Analysis All rapid torque–time variables were determined from the peak isometric torque–time curve utilizing a customized Microsoft Excel

[37,38]. A two-minute rest period was given between each angular velocity. Outcome measures included peak isometric and isokinetic knee extensor concentric torque (Nm) with the highest value of the six maximal repetitions performed used for all data and statistical analysis. 2.2.2. Data Analysis All rapid torque–time variables were determined from the peak isometric torque–time curve utilizing a customized Microsoft Excel 2016 spreadsheet (Microsoft, Redmond, WA, USA) [39,40]. Rapid torque–time outcome measures included maximum isometric knee extensor torque at 50, 100, and 200 ms from the onset of contraction (ISOM50, ISOM100,

J. Funct. Morphol. Kinesiol.2023,8, 89 4 of 14 and ISOM200, respectively) [41]. The rate of torque development (RTD) was quanti ed as the linear slope of the isometric torque–time curve (DTorque/DTime) at the follow- ing time intervals: 0–50, 0–100, and 0–200 ms from the onset of contraction (RTD0–50, RTD0–100, and RTD0–200, respectively) [41,42]. These time intervals were designated to represent early (RTD0–50) and late (RTD0–200) torque–time characteristics and are believed to characterize distinct physiological parameters [41,42]. Contractile impulse across the above-mentioned time intervals (0–50 ms, IMP0–50; 0–100 ms, IMP0–100; 0–200 ms, and IMS0–200) was quanti ed as the area under the torque–time curve ( R TorqueDTime) [43,44]. The onset of contraction was established as the moment the isometric torque produced by the participant equaled 4 Nm [42,43]. 2.3. Training 2.3.1. Sprint Interval Training Sprint interval training (SIT) took place over 12 weeks, during which participants were required to train three times per week, and consisted of maximal sprints of varying dis- tances. The total possible number of training sessions was 33 (3 sessions lost to midseason testing). SIT was performed on an outdoor grass playing eld when weather permitted and in a gymnasium during inclement weather. During training, sprint times were not recorded. However, encouragement was provided to participants during all SIT tasks by both the coaching staff and their peers. Although the rate of perceived exertion was not monitored, participants were encouraged to push themselves to maintain a rating of between 9 and 10 on the Borg Scale (0–10) throughout the duration of the SIT training. The participants continued their eld-lacrosse-speci c training with the number of practices and games varying from three to ve, and one to three per week, respectively. Sprint interval training consisted of three separate training sessions (SIT Session 1, SIT Session 2, and SIT Session 3). Sprint interval training Session 1 included maximal sprints (10–14 repetitions) at a distance of 40 m separated by 15–20 s of active recovery (walking or jogging). Session 2 involved two-three sets of all-out 15 m sprints with sets comprising 10 to 12 repetitions. Fifteen seconds of rest (no

training sessions (SIT Session 1, SIT Session 2, and SIT Session 3). Sprint interval training Session 1 included maximal sprints (10–14 repetitions) at a distance of 40 m separated by 15–20 s of active recovery (walking or jogging). Session 2 involved two-three sets of all-out 15 m sprints with sets comprising 10 to 12 repetitions. Fifteen seconds of rest (no walking or jogging) was provided between repetitions and 120 s of active recovery was utilized between sets. Lastly, SIT Session 3 required the participants to perform three to four suicides (16 m, 25 m, 50 m, 75 m) with a 60 s rest between repetitions. All SIT sessions were administered by the same member of the research team. 2.3.2. Field-Lacrosse-Speci c Training Field lacrosse-speci c training included a brief warm-up, aerobic conditioning, basic eld lacrosse skill development, tactical drills, and scrimmages (Table S1). Scheduling of practices and games followed the State High School Athletic Association calendar. 2.4. Statistical Analysis Data are presented as means standard deviations. Statistical analysis was performed using SigmaStat version 3.5 (Systat Software, Inc. San Jose, CA, USA). A Kolmogorov–Smirnov test was used to determine data normality. Results of the Kolmogorov–Smirnov tests required the following outcome measures to be assessed with non-parametric analyses: ISOM50, ISOM100, isokinetic knee extensor concentric torque at 3.14 rad s 1 , and RTD0–50. All other outcome measures were determined to be normally distributed; thus, parametric analyses were used. Changes in peak torque and rapid-torque–time variables were analyzed using a one-way repeated measures ANOVA with one within-group factor (time: preseason, midseason, and postseason). If the normality test failed (p< 0.05), Friedman repeated measures ANOVA was performed on the ranks. Secondary analysis was performed using pair-wise multiple comparison procedures with a Tukey correction. The magnitude of the responsiveness to the SIT between preseason and midseason and preseason and postseason was determined using Cohen's d effect size statistic. Effect sizes were classi ed as small

magnitude of the responsiveness to the SIT between preseason and midseason and preseason and postseason was determined using Cohen's d effect size statistic. Effect sizes were classi ed as small

This study examines the effects of sprint interval training on muscle performance in female high school lacrosse players.