Preventive Neuromuscular Training for Young Female Athletes: Comparison of Coach and Athlete Compliance Rates

A dherence and compliance are terms often used to describe the ability to follow given tasks. For neuromuscular-training (NMT) intervention studies, compliance with the protocol is an important variable when determining the success and usefulness of these programs.¹ Many groups^2–15 have measured the effect of NMT compliance in reducing knee-injury rates. Using a prospective, cluster-randomized controlled design, other investigators¹⁶ assessed compliance in 52 young female soccer teams (a total of 1055 players) who participated in a comprehensive soccer specific warm-up program called 11+. Athletes who displayed a high level of compliance showed a 35% lower overall injury incidence compared with athletes who displayed an intermediate compliance level. Similarly, athletes with a high level of compliance experienced a 39% lower incidence of acute soccer injuries than athletes with intermediate compliance levels. Authors¹ who compared anterior cruciate ligament (ACL) injury incidence rates among 6 NMT studies (using a binary incidence rate ratio analysis) found that those who demonstrated a high level of compliance had a 73% lower ACL injury incidence rate than those with low compliance levels. Their tertile incidence rate ratio analysis identified an ACL injury incidence rate in those with a high level of compliance that was 82% lower than those with moderate or lower levels of compliance. Both analyses demonstrated the effect of NMT compliance on ACL injury incidence rates.

Although past researchers^1,16 studied the effect of compliance with NMT intervention on athletic injuries, a few groups^7–11,17,18 did not report NMT compliance in the original manuscripts. Other authors^2,3 cited low NMT compliance as a limitation of their experiments that hindered outcomes. Reporting of compliance and the effect of NMT compliance are not well documented, are often neglected in analysis, and are not emphasized in most study designs. There is no standard reporting method for compliance rate in NMT research, which may be why this factor is not often reported.

Therefore, we sought to analyze 2 types of compliance measures: compliance of coaches with the given study protocol and compliance of athletes with the given NMT interventions. The current study with 2 arms (experimental versus control group) was performed as a secondary analysis to determine the prophylactic effectiveness of preventive NMT on knee injuries in young female athletes. Our main purpose was to analyze compliance with a preventive NMT protocol in coaches and athletes by (1) descriptively analyzing coach and athlete compliance with the study protocol, (2) examining coach and athlete compliance between the study arms, and (3) comparing coach and athlete compliance based on school level and sport.

METHODS

Compliance Rate Calculation

The compliance calculation started with the first intervention session of the preseason and continued through the last intervention session of the in-season. Each intervention provider's compliance was examined based on the study protocol (3 times per week during the preseason and 2 times per week in-season) and how many times the intervention was delivered. The coach compliance rate was defined as follows:

Coach compliance (%) = Summation of intervention sessions delivered during preseason and in-season/summation of maximum intervention sessions that could be delivered according to the study protocol.

Individual athlete compliance was believed to be the most reflective variable of NMT activity engagement. The individual athlete compliance form is shown in Table 1 and was completed by intervention providers each time the intervention was delivered. The individual athlete compliance was calculated as follows:

Table 1.  Example of Individual Athlete Compliance Form

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Athlete compliance (%) = Proportion of individuals on roster who attended and completed more than 2/3 of intervention sessions that were delivered by intervention providers during preseason and in-season.

We selected the cutoff value of 2/3 of intervention sessions because previous authors¹ indicated that once compliance with NMT decreased to 2/3, NMT was not prophylactically effective.⁴

Statistical Analysis

All teams were randomized, and characteristics of each group (core integrative versus speed and agility training) are listed in Table 2. Independent t tests were performed for height, weight, body mass index, and age. The α level for the independent t test was set a priori at .05.

Table 2.  Demographic Information for Experimental and Control Groups

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For aim 1, we used descriptive statistics to analyze coach and athlete compliance rates between the study arms. To examine aim 2, independent t tests were performed to examine differences in coach and athlete compliance rates between the study arms, and the a priori α level was set at .05. To attain aim 3, both compliance rates were analyzed based on school level (middle or high school) and sport (basketball, soccer, or volleyball) using a 2-way analysis of variance. Bonferroni post hoc tests were employed to adjust for multiple comparisons.

RESULTS

A total of 30 teams (12 basketball, 6 soccer, and 12 volleyball teams) were assigned to the core integrative NMT group and 22 teams (11 basketball, 5 soccer, and 6 volleyball teams) were assigned to the speed-and-agility training group (Figure).

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Group Demographic Descriptive Statistics

Demographic descriptive statistics for the groups are found in Table 2. Height, weight, body mass index, and age did not differ on pretest measures.

Aim 1: Coach Compliance With Protocol

Coach compliance with the given protocol was 52.5% ± 11.7%. The intervention was implemented at a mean rate of 1.3 ± 1.1 times per week during the preseason and 1.2 ± 0.5 times per week in-season.

Aim 1: Athlete Compliance With Intervention

Athlete compliance with the intervention was 87.8% ± 10.6%. During the study, 88.4% of athletes completed more than 2/3 of all the intervention sessions.

Aim 2: Coach Compliance Between the Experimental and Control Groups

Coach compliance was greater in the core integrative NMT group than in the speed-and-agility training group (P = .014; Table 3). Coach compliance during the preseason did not differ between groups; however, greater compliance was recorded in-season for the core integrative NMT group compared with the speed-and-agility training group (P = .022; Table 3).

Table 3 Intervention Sessions Performed and Coach Compliance in Experimental and Control Groups

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Aim 2: Athlete Compliance Between the Experimental and Control Groups

Athlete compliance did not differ between the core integrative NMT and speed-and-agility training groups (P = .602; Table 4).

Table 4.  Athlete Compliance in Experimental and Control Groups

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Aim 3: Coach Compliance Based on School Level and Sport

There was no interaction between school level and sport (P = .348; Table 5) and no main effect of sport (P = 0.867; Table 5). However, coach compliance was greater in middle schools than in high schools (P = .001; Table 5).

Table 5.  Intervention Sessions Performed and Coach Compliance By School Level and Sport,^a Mean ± SD

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Aim 3: Athlete Compliance Based on School Level and Sport

There was no interaction of school level and sport (P = .833; Table 6) and no main effect of school level (P = .359; Table 6) or sport (P = .733; Table 6).

Table 6.  Athlete Compliance By School Level and Sport,^a Mean ± SD (%)

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DISCUSSION

The main purpose of our study was to analyze coach and athlete compliance with interventions designed to reduce traumatic knee injuries in young female athletes. Coach compliance with the protocol was 52.5% ± 11.7%, which is a mean rate of 1.3 ± 1.1 times per week during the preseason and 1.2 ± 0.5 times per week in-season. The study protocol was to provide the assigned intervention 3 times per week during the preseason and 2 times per week in-season. The rate of the intervention as instructed by the coach was unexpectedly lower. Low levels of compliance with NMT protocols were documented in past investigations.^2,3 One strategy used in previous work to enhance compliance with NMT was to have noncoaching personnel take a supervisory role in the interventions.² In our study, most of those who provided the intervention were coaches (n = 39, 83%); 8 intervention providers were noncoaching staff members (4 certified athletic trainers and 4 undergraduate college students). Thus, we assessed whether the teams under the noncoach intervention providers demonstrated higher compliance. However, compliance with the assigned intervention did not differ for coach versus noncoach intervention providers (57.3% ± 14.5% led by coaches versus 53.3% ± 23.0% led by noncoaches, P = .638). One certified athletic trainer in this study mentioned that the assigned intervention was sometimes omitted at the coaches' discretion even though the athletic trainer was available to deliver the prescribed intervention. This comment exemplified that some coaches chose not to follow the protocol and that coaches have strong authority to determine how practice time is used. Therefore, gaining coaches' understanding through communication is a key to successful implementation of the protocol.

The different levels of coach compliance between the study arms were not expected. In this study, the speed-and-agility training intervention served the purpose of sham training because the randomization was performed at the team level but not at the school level. Previous researchers²⁵ reported an increase in sprint start speed after the speed-and-agility training program. The exercises incorporated in the speed-and-agility training program placed more emphasis on the performance aspects of training, so we expected better coach compliance with this group. However, the core integrative NMT intervention was practiced a total of 20.4 times in the experimental group compared with 15.7 times by the speed-and-agility training group during a season (Table 3), and the difference appears to stem from the in-season compliance rates. The core integrative NMT intervention was performed approximately 15 times in-season (mean of 1.3 times per week; Table 2), yet the speed-and-agility training intervention was implemented only 11 times in-season (mean of 1.0 time per week; Table 3). Given the lack of difference in the number of interventions implemented between the study arms during the preseason, the in-season compliance rate difference likely influenced the overall season compliance rates (Table 3). According to our research associates working on site, a few coaches commented that limited practice schedules did not allow them to follow the study protocol (3 times per week during the preseason and 2 times per week in-season), especially in-season. The reasons for the limited practice schedules varied, but the most common reason was tight competition schedules. For instance, when 2 competitions were scheduled during weekdays, only 3 days were available to perform the prescribed intervention, but 1 or 2 of those days were often used for rest and recovery, which made following the in-season protocol (2 times per week) difficult. For this reason, we carried out an extra analysis to investigate if the number of athletic competitions between the study arms differed. Indeed, the speed-and-agility training group had more athletic competitions (an average of 24.0) compared with the core integrative NMT group (an average of 22.4; Table 7). Therefore, more athletic competitions might have reduced opportunities to perform the speed-and-agility training intervention in the control arm, which in turn might have led to the higher level of coach compliance in the experimental arm.

Table 7.  Athletic Competitions of Experimental and Control Groups, Mean ± SD

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In addition, coach compliance levels were different between the school levels but not different by sport (Table 5). The lower coach compliance levels at middle schools across all sports might be due to fewer practice opportunities compared with high schools during the preseason. In this study, a few middle school soccer and volleyball coaches mentioned that they did not have adequate time to perform the assigned interventions during the preseason. Specifically, the preseason duration of the soccer and volleyball teams at the middle school level was approximately 2 weeks compared with 4 weeks for the basketball teams, which reflected the observed results within the middle schools (Table 5). The same explanation might be applicable to the differences in coach compliance between the middle and high schools. The high school preseason is generally longer than that in middle school, so high school coaches might have had more time and opportunities to perform the assigned interventions. On the other hand, middle school coaches preferred not to spend limited practice time and opportunities on the study interventions. In short, it appeared that available time during the season plays a critical role for coaches. The analysis of coach compliance between the study arms showed the same tendencies. The tight schedules and greater number of competitions seemed to limit opportunities to perform the speed-and-agility training in the control arm. Therefore, securing available time is another important aspect to enhancing compliance with a study protocol and implementation of preventive NMT.

Athlete compliance did not differ between the study arms (Table 4). Nearly 90% of athletes who were enrolled in this clinical trial participated in more than 2/3 of the intervention sessions given, regardless of school level or sport (Table 6). The main reasons for missing the assigned NMT were being late for practices and being sick or injured. Our results offer important clinical implications: when the intervention was provided by the coaching staff, most athletes followed their instructions. Authors^2,3 of several previous preventive NMT studies have pointed out that compliance is a limitation. However, because most athletes tend to perform prescribed interventions, a key to enhancing preventive NMT compliance is to enhance coach compliance and adherence to the intervention. Researchers²⁶ who investigated variables influencing the implementation of preventive NMT reported that coaching experience and the presence of additional supporting staff (such as an athletic trainer or strength and conditioning specialist) may influence participation. Thus, the presence of supporting health care providers is a critical element in preventive NMT implementation and execution. In addition, these authors²⁶ found that performance enhancement, educational requirements, and policy changes by athletic associations were key to implementing preventive NMT intervention and maintaining high compliance among coaches. Steffen et al²⁷ recently compared 2 preventive NMT delivery methods: (1) a set of educational workshops for coaches and on-site assistance from physiotherapists and (2) unsupervised Web site-based education for coaches. Preventive NMT exercises were practiced almost twice as much by teams whose coaches took the educational workshops and had assistance from physiotherapists compared with teams whose coaches had access to the unsupervised Web site-based education. Also, athletes who adhered to the preventive NMT exercises at the higher level had a 57% lower injury incidence.²⁷

Our study had several methodologic concerns that need to be reported. First, the cluster randomization resulted in almost equal numbers of basketball and soccer teams between the arms; however, randomization was not ideal in volleyball. Only 6 teams were allocated to the speed-and-agility training group compared with 12 teams in the core integrative NMT group (Figure). Second, cross-contamination between the training groups occurred. Several athletes were recruited to more advanced teams during the intervention period, which resulted in several participants experiencing both interventions. Because the analysis was performed under the ITT principle, we analyzed the data according to the team of initial allocation.

CONCLUSIONS

This project focused on analyzing 2 types of compliance: compliance of intervention providers with following a study protocol (coach compliance) and compliance of individual athletes with performing assigned NMT (athlete compliance). Coach compliance with the study protocol was approximately 50% and was greater in the experimental arm than in the control arm. High school coaches were more compliant than middle school coaches. Coach compliance did not differ among sports. Nearly 90% of athletes complied with more than 2/3 of the interventions, regardless of study arm, school level, or sport, which indicates that athletes can follow a given intervention. Busy competition schedules and a lack of available time during seasons might have contributed to the lower compliance level of coaches. Because previous researchers identified an inverse dose-response relationship between preventive NMT compliance and traumatic knee (ie, ACL) injury,^1,14,28 future investigators need to focus on finding practical strategies to make NMT a part of regular practice regimens. This will allow coaches to comply with and adhere to preventive NMT, which may protect young athletes from injury.