Effect of fatigue caused by a simulated handball game on ball throwing velocity, shoulder muscle strength and balance ratio: a prospective study

Participants

Participants in this study comprised a convenience sample of 10 highly trained, competitive, professional male handball players from Brazil. The players had a mean age of 23.1 ± 2.8 years (range: 20–29 years), mean height of 185.0 ± 7.7 cm (range: 172–193 cm), and mean body mass of 87.1 ± 11.3 kg (range: 66–105 kg). All participants were recruited from an elite team that participates in national and international championships and had engaged in handball training for a mean of 10.2 ± 4.0 years (range: 5–18 years). Exclusion criteria were shoulder pain or injury within the year leading up to the study. Four athletes had shoulder injuries predating this time period.

Participants were informed of the potential risks and benefits of the study and signed an informed consent form to take part. All experimental procedures were approved by the Federal University of São Paulo Human Research Ethics Committee and conformed to the principles outlined in the Declaration of Helsinki.

Study design

Upon arrival at the laboratory, participants underwent isokinetic evaluation of their dominant upper limb. Tests began at 2 pm for all the athletes in order to avoid the influence of the circadian rhythm on muscle strength [22]. Limb dominance was determined by identifying the upper limb that the participant prefers to use to throw a ball [23]. Ten minutes after isokinetic evaluation, the participants performed eight standing and eight jumping arm throws on the handball court to measure ball velocity.

Immediately after completion of the throwing activities, athletes performed a program of simulated game activities (SGA) to simulate the upper limb muscular stress of a real handball game. Five minutes after the end of the SGA, arm throwing action was repeated to measure ball velocity . Finally, the athletes were submitted to another isokinetic strength test. All the evaluation tests were done in this sequence and on the same day.

Isokinetic assessment

Before isokinetic testing, a 5-min warm-up was performed on an arm-cycle ergometer (Cybex Inc., Ronkonkoma, NY, USA) at a resistance level of 25 W, and standardized static stretching exercises were performed, since it has been demonstrated that these static exercises in association with warm-up exercises performed prior to isokinetic strength tests have no influence on strength results [24, 25]. To stretch the glenohumeral joint muscles, the following exercises were performed in this order: arm abduction at 90 deg with horizontal flexion targeting the posterior deltoid fibers; shoulder abduction with the upper limb behind the head targeting the triceps muscle; upper limb abduction to 135 deg with horizontal extension targeting the pectoralis major muscle; upper limb abduction at 90 deg with horizontal extension targeting the pectoralis minor muscle; and shoulder internal rotation with the hand behind the body targeting the external rotator muscles. All the static stretching exercises were performed in two unassisted successive repetitions for 15-s up to a threshold of mild discomfort, with no pain acknowledged by the athletes. Between each stretching repetition, during stretching exercises and at each muscle group change, the upper limb was rested for a 15-s period in a neutral position. Following the stretching period, participants were placed in the isokinetic dynamometer (Biodex Medical Systems Inc., Shirley, NY, USA) to evaluate maximal strength during positive (concentric) and negative (eccentric) exercises for the dominant limb [26].

The IR and ER muscles were assessed in the seated position, with the upper limb abducted at 90 deg on the frontal plane and the elbow flexed at 90 deg. The range of motion reached 50 deg for internal rotation and 70 deg for external rotation. The isokinetic velocities selected were 60 deg∙s⁻¹ and 300 deg∙s⁻¹ in the concentric mode (positive exercise) and 90 deg∙s⁻¹ and 300 deg∙s⁻¹ in the eccentric mode (negative exercise). Participants performed three submaximal trials to familiarize themselves with the range of motion and the accommodating resistance of the dynamometer. Participants then performed a maximum of five repetitions to test each velocity used. Positive exercise tests were done first; lower test velocities were performed before faster velocities. Peak torque, total work, and conventional strength ratio (calculated as positive external rotation-to-positive internal rotation ratio) was assessed at 60 deg∙s⁻¹, peak torque and average power was assessed at 300 deg∙s⁻¹, and functional strength ratio was calculated as negative external rotator peak torque at 90 deg∙s⁻¹ to positive internal rotator peak torque at 300 deg∙s⁻¹. Successive velocity testing was separated by one-minute rest intervals.

Before testing, the dynamometer was calibrated according to the manufacturer’s specifications and checked prior to testing each participant. Standardized verbal encouragement was given during all testing. Visual feedback from the computer screen was not allowed.

Throwing performance

Ball velocity was measured by a radar gun (Stalker Sport, Stalker Radar, Texas, USA) according to Cools et al. [27]. To this end, participants performed two types of throw: one was in a standing position seven meters from the goal; the second (from the nine meter line) was a jumping throw preceded by two steps. All participants threw the ball in this order, and performed eight arm throws in a standing position and eight in a jumping position, two into each corner of the goal. Ball velocity was measured for all arm throws, where the velocity used was the mean of the eight throws. This test was performed on an official handball court.

To establish test-retest reliability, subjects were invited to participate in a second measurement session at 3–4 days after the initial assessment, during which ball velocity on both tests was assessed in the same way as in the first session. A time interval of 3–4 days was chosen to avoid the training effect.

Simulated game activities (SGA)

Simulated game activities were designed to simulate the upper limb muscular stress of a real handball game. The SGA were based on the mean number of steps and throws toward goal registered for each team player position in the last three games. Therefore, the exercise protocol devised included 100 steps and 20 arm throws at goal.

During the SGA, the heart rate (HR) of all participants was monitored using a heart rate monitor (Suunto Team Pod, Suunto Oy, Vantaa, Finland) with the purpose of monitoring exercise intensity. The mean HR during SGA was 153 ± 13 bpm, which represents approximately 77 % of the maximal predicted HR (220-age) [28] for the group of handball players.

Statistical analysis

All variables presented normal distributions according to the Shapiro-Wilk test. In the pre-SGA condition, the association between ball velocity and isokinetic muscular performance was evaluated by calculating Pearson’s correlation coefficients (r) and classifying according to the following rule: no correlation for r < 0.50; moderate for 0.50 ≤ r < 0.75; and good-to-strong for r ≥ 0.75 [29].

Paired t-tests were used to compare the effect of SGA on isokinetic muscular strength and ball velocity. The significance level (α) was set at 0.05 for all statistical procedures. The results were also assessed for clinical significance by using effect size (ES) of changes. ES was calculated and classified as follows: large for ES ≥ 0.8, moderate for 0.5 ≤ ES < 0.8, small for 0.2 ≤ ES < 0.5 and trivial for ES < 0.2 [30]. Confidence intervals (90 %) were also calculated. All statistical analyses were performed with Statistica version 7.0 software (Statsoft Inc., Oklahoma, USA).

An intraclass correlation coefficient (ICC) was used to assess test-retest reliability of both ball velocity tests (jumping or in standing position). ICC values of less than 0.40 were considered poor, 0.40–0.59 fair, 0.60–0.74 good, and .075–1.0 excellent [31].