We will conduct a randomized, placebo-controlled clinical trial with parallel groups at Universidade Estadual Paulista (UNESP), Presidente Prudente, SP, Brazil. The trial has been prospectively registered at ClinicalTrials.gov (NCT02918916) and approved by Human Research Ethics Committee of UNESP, Presidente Prudente, SP, Brazil (1.389.046/2016). The study follows the SPIRIT 2013 checklist (Standard Protocol Items: Recommendations for International Trials)25 and TIDieR (Template for Intervention Description and Replication)26 to improve the information and quality of intervention reporting.27 Prior to the procedures, the participants will receive oral and written instructions and sign a consent form agreeing to participate in the study. All personal data will be confidential.

Participants will undergo a 12-week training program divided into two phases. In phase 1 (six weeks), participants will undergo training consisting of sprints and squats in the same session. After this period, the participants will undergo new tests and be randomly allocated into the groups that comprise the study. In phase 2, a new six-week training period will begin. In this phase, the participants will train normally with the adjusted loads and between sprints and squats will receive the recovery strategy related to the group to which they belong.

A flowchart of the design, composition of the groups, and phases is presented in Fig. 1.

Figure 1.

Study design.

(0.22MB).

A total of 45 healthy male volunteers will be recruited from the local university (UNESP) via online media advertisement, personal invitation, telephone, and SMS and registered in the database of the Sports Physical Therapy Laboratory. These procedures are recommended by Treweek et al.28 as a strategy to improve participant recruitment.

Initial contact with all participants will be made by telephone to establish their willingness to participate and a meeting will be scheduled to evaluate the eligibility criteria.

The following inclusion criteria will be employed:

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  Healthy patient (self-report);

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  Male gender;

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  Age between 18 and 30 years.

Participants with the following will be excluded from the study:

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  History of cancer;

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  Presence of anemia, inflammation, or diabetes;

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  History of muscle injury in the lower limbs or spine in the previous six months.

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  Occurrence of musculoskeletal injury during the study.

Participants will be instructed to maintain their daily diet routine and abstain from anti-inflammatory and analgesic drugs, as well as any exercise not presented during the study. This information will be reinforced during data collection and monitored by self-report to further analysis.29

Participants will be randomly allocated to the groups after phase 1. The stratification process will be carried out based on the concept of responders and non-responders to adaptation capacity,30 defined in this study as functional and clinical responses. Each response will be recorded before and after phase 1.

Adaptation capacity (AC) will be extracted using the following equation:

Functional parameter (FP)

A priori knowledge will be used based on the study of Kotzamanidis et al.,31 who observed average gains of 8.5% after combined training. This value is set as the ceiling of strength gain capacity. Therefore, gains ≥8.5% in strength test will correspond to 100% of FP and gains <8.5% will be inserted into the following equation:

The primary outcome will be the peak torque obtained in the maximal voluntary isometric contraction. Secondary outcomes are other functional, clinical, and psychological outcomes and VEGF, described below. Data will be collected in a specific time point (Table 3). Each assessor will be responsible for the same outcome throughout the study. Performance tests will be completed in two sessions separated by a day of rest and will be performed in the order described below.

In the first session, the sprint test, squat jump, and maximal incremental test will be completed. In the second session, the strength and power tests and maximal voluntary isometric contraction (MVIC) will be performed. Additionally, care will be taken to allow sufficient rest (15min) between all tests on the same day to limit the effects of fatigue on the following test. This rest is based on time to recovery of each test.37–41

There will be 12 secondary outcomes to understand the comprehensive process of post-exercise recovery and performance.

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  Strength and power testing: these tests will be carried out with a bar.35 Participants starting in the upright position with the bar in contact with the shoulders and will be required to perform the squat with continuous movement until their thighs reach the horizontal plane, then immediately perform the reversed motion at maximum speed. Information about the eccentric distance reached and concentric speed of each repeat will be recorded by a linear velocity transducer (T-Force System Ergotech, Murcia, Spain), which will also provide visual and auditory feedback.

  For the strength test, the warm up will consist of 10 repetitions at 40–60% of maximum perception. The last acceptable repetition with the highest possible load will be considered 1RM (repetition maximum). The rest period between sets is two minutes.

  To determine the velocity of displacement during the concentric phase of full squat, the load will be adjusted until the highest velocity is obtained. The velocity index is calculated by the average value of peak velocity obtained with each load. The tests will be carried out gradually and with increments of 10kg for each set with two trials executed with each load.

  For the power test, the warm up will consist of five repetitions with the bar. Bar displacement and peak and mean velocity will be recorded by an encoder. A computer program (Isocontrol Dinámico, 3.6, Spain) will be used to calculate the velocity of displacement for each repetition throughout the range of motion. An interval of 2–3min will be given between trials. The best trial with each load will be recorded.

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  Maximal incremental test: the maximum oxygen consumption (VO2max) and maximum aerobic speed (MAS) will be determined on a treadmill (Inbramed, Inbrasport, Brazil) using an incremental protocol.42 Participants will do a five-minute warm up at 7kmh−1. After five minutes of rest, the participants will perform the incremental protocol consisting of running at a starting velocity of 10kmh−1, with increments of 1kmh−1 per minute until exhaustion and a fixed inclination of 1%. The test will finish through voluntary exhaustion or the presence of clinical alterations. Gas analysis will be measured continuously and the average value of every 30s will be recorded (VO2000, MedGraphics, Minnesota, USA). The MAS will be recorded as the speed corresponding to the final complete step in the incremental test.

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  Squat jump: participants will remain with the sole of their feet in contact with the jump platform (Multisprint, Hidrofit, Brazil), legs at 90° of flexion, hands on hips, trunk upright, and without previous movements. The participant will perform a jump keeping their legs straight (180°) and touch the platform again. Each participant will perform three complete tests with a 30-second rest interval.43 The best measure of the tests will be adopted.

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  Sprint test: participants will perform three maximum sprints exceeding 30m with 3-min rest intervals. Performance times at 10, 20, and 30m will be recorded (Multisprint, Hidrofit, Brazil).35 The average of the two best tests will be adopted.

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  Muscle soreness: values of muscle soreness in lower limbs will be obtained through an 11-point visual analog scale (VAS),17 with ‘zero’ corresponding to absence of soreness and ‘10′ to the maximum level supported by the participant.44

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  Pain threshold: pressure algometry will be applied at five specific sites of the quadriceps in the dominant leg.45 Participants will be instructed to signal when the pressure sensation becomes discomfort. The pressure will not exceed 2.55kgf.46

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  Perception of exertion: the level of exertion reported by participants will be assessed using the Borg Scale (6–20 points), with ‘six’ corresponding to ‘very easy’ and ‘20′ to ‘exhaustive’.47

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  Perception of recovery: the level of perception of recovery will be assessed by a 10-point Likert scale, with ‘one’ corresponding to ‘not recovered’ and ‘10′ to ‘fully recovery’.29,32

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  Psychological questionnaire: participants will be instructed to mark an “X” on a 10-cm visual analog scale, with ‘zero’ corresponding to ‘least possible’ and ‘10′ ‘most possible’ for each rating (readiness for exercise, fatigue, vigor, sleepiness, and pain).48

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  Belief questionnaire: after phase 1, participants will answer a belief questionnaire to measure their ‘belief’ in the effectiveness of the technique. Participants will be instructed to mark an “X” on a 5-point Likert scale, with ‘zero’ corresponding to ‘not effective’ and ‘10′ to ‘extremely effective’. After application of the recovery techniques, the participants will complete a similar questionnaire to measure their perceived effectiveness of the technique.48

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  Vascular endothelial growth factor (VEGF): 10ml of blood will be collected and plasma from this sample will be stored at −80°C for later analysis. The plasma level of VEGF will be analyzed using the ELISA method (enzyme-linked immunosorbent assays) following the manufacturer's instructions (RayBio, Norcross, GA, USA).49

This study will ensure that assessors will be blinded. Although the therapist is not blinded, he will not have access to which recovery strategy is being applied (phototherapy or placebo). One participating researcher will be responsible for programming the phototherapy device based on random allocation. In this study design, it will not be possible to blind the participants and therapists due to the control condition.

Based on data from a previous study4 that used the same light source of phototherapy, for a three-arm parallel study (with SD=38.86Nm on MVIC with α=0.05 and β=0.8, to detect a difference of 10%) a total sample of 45 will be required, allowing for sample loss.

The statistical analysis will be conducted in SPSS (version 18; SPSS Inc., Chicago, IL, USA). After the adaptation process, the data will be analyzed as described below.

For outcomes with two time points: analysis of covariance (ANCOVA) with general linear models will be used to test between-group differences, with the difference/delta value as a dependent factor, group variable as fixed factor, and baseline values as covariate. (Outcomes: performance tests, VEGF, belief questionnaire, perception of exertion.)

For outcomes with three or more time points: initially, sphericity of the data will be tested by Mauchly's test. In case of violation of the sphericity assumption, the Greenhouse–Geisser corrections will be used. Analysis of variance (ANOVA) with repeated measurements will be used to test between-group differences followed by Bonferroni or Dunn post hoc test. (Outcomes: perception of recovery, psychological questionnaire, muscle soreness, and pain threshold.)

The data will be double entered. All participants will be included in the analyses following an intention-to-treat approach and the significance level will be set at p<0.05.