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Participants
Fourteen semi-professional female field hockey players took part in this study (age: 22.6 ± 4.9 years; weight: 63.4 ± 5.8 kg; height: 167.0 ± 0.1 cm; body mass index: 22.6 ± 1.7; field hockey training experience: 12.9 ± 5.8 years; training per week: 8.7 ± 1.1 hours included technical/tactical and physical training, divided in 3 days per week). All the female field hockey players played in a semi-professional team that competed in the 2nd Division of the Spanish Female Field Hockey League. Exclusion criteria were a) goalkeepers, b) female field hockey players who were not able to perform the test due to an injury, sickness, or any physical complaint were excluded from the final sample of this study. All players received information of the neuromuscular test battery procedure and signed a consent form for participating in this study. The experimental procedure of this study was in accordance with the guidelines outlined in the Declaration of Helsinki 2013 and was approved by the University Francisco de Vitoria Ethics Committee (number 45/2018).
Experimental design
The current investigation is a cohort study, planned to be conducted monthly throughout the duration of the 2019–2020 season. However, the appearance of the COVID-19 pandemic in March 2020, caused the training and competition to be stopped immediately. Since the Spanish field-hockey season is paused during the winter months of January and February (an indoor competition is played during this time), data was recorded only from September 2019–December 2019. Thus, the assessments were performed at four different separate time points during the competitive season (Fig. 1): September 2019 (i.e., 3 weeks after the preseason period); October 2019 (i.e., after completing the first four matches of the season); November 2019 (i.e., after completing seven official competitive games); December 2019 (after completing the 11 official competitive games), a schedule which was predetermined based on player availability and match schedule. The players were tested before the training session, on the last day of the month in a physiotherapy room at the training facility of the field hockey club.
During each testing session, hockey players participated in anthropometric measurements, ROM tests (i.e., ankle dorsiflexion and straight leg raise test), and maximal isometric muscle strength tests (i.e., hip adduction and abduction and knee flexion) in their dominant and no dominant limbs). Also, fluctuations in their neuromuscular performance (i.e., measured by countermovement jump) were recorded. All testing were conducted by two senior sports physiotherapists (i.e., with 10 years and 6 years of experience respectively).
Perceptual fatigue was measured using a perceived well-being questionnaire recorded before each training session [13] to detect fatigue status and the mean for each session/week was recorded for subsequent analysis. In addition, each month female hockey players filled injury questionnaire and all the measurements were undertaken at the same time of the day (i.e., to avoid the influence of circadian rhythms) on neuromuscular performance that has been reported in other female team sports [14].
Before each testing session, female field hockey players conducted a standardized warm-up that consisted of 5 min of jogging, 5 min of dynamic stretching and joint mobility exercises [15]. All the female field hockey players were previously familiarized with the testing procedures because the muscle strength test employed in this investigation was part of an ongoing injury preventive program employed by the club which had been initiated a few months before this study. Based on the recommendations of Wollin et al. [15] the order in which the players were tested, and the selection of the tested leg were chosen randomly. Limb dominance preference was determined through a questionnaire. To minimize interference from uncontrolled variables, subjects were instructed to maintain their usual lifestyle and normal dietary intake on the days of measurement and to refrain from caffeine intake 24 h before the experiment [16].
Isometric knee flexion torque
Maximal isometric muscle knee flexion strength of hamstrings on both sides was measured using the previously described methodology [17] with a portable handheld dynamometer (Nicholas Manual Muscle Tester; Lafayette Indiana Instruments, Lafayette, IN, USA). For this measurement, each player was positioned in a prone position on a bench, with 15 degrees of knee flexion. The examiner (first physiotherapist) placed the dynamometer in the distal portion of the sural triceps using external belt fixation according to previous reported [18, 19], while the assistant (second physiotherapist) held the subject’s pelvis over the sacrum, to prevent elevation during the test. The examiner requested a knee flexion with the intention to bring the heel of the foot to the buttock. Female field hockey players performed voluntary contractions for a maximum of 5 seconds against the dynamometer and repeated the exercise twice for each leg. There was a rest period of 30 seconds between each measurement [18] and two repetitions were performed for both the dominant and non-dominant leg. The highest value obtained was recorded for subsequent analysis. The ICC for this test was 0.82 [19].
Isometric hip abductor and adductor torque
Maximal isometric strength of the hip abductors and adductors on both sides was measured using a portable handheld dynamometer (Nicholas Manual Muscle Tester; Lafayette Indiana Instruments, Lafayette, IN, USA). Female field hockey players were in a supine position with their hips in a neutral position and told to stabilize by holding onto the sides of the table. The first physiotherapist applied resistance in a fixed position, 5 cm to the proximal edge of the lateral for abduction or medial for adduction malleolus fixated with a rigid belt around the legs as previously reported [20], while the second physiotherapist maintain the correct position of the patient. Female field hockey players performed voluntary contractions for a maximum of 5 seconds against the dynamometer and repeated the exercise twice for each leg There was a rest period of 30 seconds between each measurement [21, 22]. Two repetitions were performed for both the dominant and non-dominant leg. The highest value obtained was recorded for subsequent analysis. The ICC for this test was 0.93–0.97 [20].
Hip flexion range-of-motion (straight leg raise test)
To measure the flexibility of the hamstrings through hip flexion ROM with the knee extended, the straight leg raise test was performed [18, 23]. An ISOMED Unilevel inclinometer (Portland, Oregon) with a telescopic extension long arm was used for the measurement. The inclinometer was placed approximately on the external malleolus and the distal arm was aligned parallel to an imaginary bisecting line of the limb [24]. The test ended with one or more of the following criteria: a) The examiner was unable to continue the joint movement evaluated, due to the high resistance developed by the stretched muscle group; b) The examinee reports a significant sense of distrust; c) noted compensations that could increase the measurement; d) the appearance of pain. The ICC for this test was 0.93–0.97 [25].
Ankle dorsiflexion range of motion (ROM)
Unilateral ankle dorsiflexion ROM was measured using the LegMotion System (LegMotion, Check your Motion, Albacete, Spain). Each female field hockey players took a standing position on the LegMotion System with their hands on the hips and the foot of the ankle being tested placed on the measurement platform. The contralateral foot was positioned off the platform with the toes positioned at the edge of the platform. While maintaining this position, players were instructed to flex the knee on the same leg as the tested ankle, with the knee contacting a metal stick placed in front of the toe. Once contact between the knee and stick, and between the heel and ground, were maintained for 3 s, the stick was progressively moved away from the knee in 1-cm increments each time until the knee could not contact the stick or heel contact with the ground could not be maintained [24] The furthest achieved distance (cm) of the metal stick from the closest toe was recorded. Two attempts were permitted for each ankle (dominant and non-dominant legs) with 10 s of passive recovery administered between attempts. The dominant leg for each player was determined as their preferred leg for kicking a ball [26, 27]. Additional attempts were performed until two ankle dorsiflexion measurements with less than 10% difference for each ankle were attained. The highest value of the two attempts for each ankle was used for further analysis. The ICC for this test was 0.96–0.98 [26].
Countermovement jump
Vertical jump height was measured following established procedures [28]. For measuring each jump a validated contact platform was used (Chronojump Boscosystem®, Barcelona, Spain) [29]. Specifically, female field hockey players performed a countermovement jump without arm swing with their hands on their hips. Each player performed two maximal attempts, with each attempt interspersed with 45 s of passive recovery. Additional attempts were performed until two jumps differed in height by less than 10% for each jump type. The greatest jump height (cm) for each jump type was used for analysis. The ICC for this test was 0.90 [30].
Perceived well-being questionnaire
Perceptual responses were measured using a psychological questionnaire developed by McLellan et al. (2010) designed to assess perceived well-being questionnaire (5-WQ). Field hockey players completed a 5-item psychometric questionnaire that included questions generally related to fatigue, perceived levels of sleep quality, muscle pain, stress level, and mood. A five-point Likert scale (i.e., values of 1–5 with 0.5 point increments) was used. Perceived well-being questionnaire was determined by summing the 5 questions to obtain a score ranging from 5 to 25 [13].
Statistical analysis
Given the observational design and exploratory nature of the study involving volunteer participants, a priori sample size estimates for hypothesis testing were not carried out. However, where differences in the measured variables were observed over time, the magnitude of the effect size and p-value are reported.
Shapiro–Wilk test was first used to assess the normal distribution of data. The means and standard deviations of the data were determined. These were compared for the ROM, strength, countermovement jump and perceived well-being test variables registered in four different months (September, October, November, and December) using a repeated-measures analysis of variance (ANOVA). If significant differences were found between the measures across the four instances, a Bonferroni post hoc test was performed. In cases where the sphericity assumption was violated, a Greenhouse–Geisser adjustment for p-values was reported. The effect sizes of the repeated measures ANOVA were measured using partial ηp2 values, and the following thresholds were used: trivial (ηp2 ≤ 0.01), small (0.01 ≤ ηp2 < 0.06), medium (0.06 ≤ ηp2 < 0.14), and large (ηp2 ≥ 0.14).
Perceived well-being values were compared using the non-parametric Friedman’s test of repeated measures, and effect sizes were determined using Kendall’s coefficient of concordance (Kendall’s W), the following thresholds were used: trivial (W ≤ 0.1), small (0.1 ≤ W < 0.3), moderate (0.3 ≤ W < 0.6) and large (W ≥ 0.6). Significance was set at p < 0.05. Statistical analysis was carried out using Jamovi (version 2.3.12, www.jamovi.org).
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