Objectives :

To determine intra and inter-subject sprinting performance modifications with trademarked Carbon-made spiked-Shoes (CS) compared to usual carbon-free ones (Standard spiked-Shoes-SS).

Methods :

Design. Multiple N-of-1 trial (Alternating Treatments Design), with block randomisation and double blind procedure. For each participants, sixteen repetitions of 30m-sprint are applied either with CS or SS, in random order for each repetition, during a 3h session a day. Blind procedures are reached by applying a dark sleeve cover on each shoes, and by separating raters from investigators.

Patients. Regional to National healthy sprinting athletes (750 IAAF/WA points), affiliated to the French Athletics Federation among the South Regional Athletic League (Comité du Var-FFA), are recruited as volunteers, with their own CS (from the same brand for homogeneity and generalisation concerns) and SS.

Main criteria. Time on a 30-meters sprint, with Force-Velocity Profiling (FVP) procedure, using Stalker Sport radar.

Secondary outcome measures. F0, V0, Vmax, Pmax , DRP and other standard FVP parameters, also measured with MySprint software; morphometric and cinematic data ; mean price difference between the two models.

Statistical analyses. A block randomisation model will be applied to check for the randoms size; variance analysis with a mixt linear model will be applied for group and confounding factors analysis. Student-T test and NAP will be applied for intra-individuals analysis.

Setting. The medical commission of the Var Athletics Committee (VAC), composed by medicine doctors, physiotherapists, universitary sport-scientists and FFA coaches, was in charge of the project, at Toulon conurbation and Draguignan, France.

Design. N-of-1 Trials is the usual term for randomized, double-blind SCEDs. This one has been designed as an Alternating Treatment Design (ATD), one of the four SCEDs types 25.

Due to the strict " on-off " intervention effect, no potential interference was expected between phases, and a " best treatment " final phase seems not necessary in the absence of carry-over or interaction effects. After discussion with coaches and athletes, the main constraint was to respect a single day " standard " short-sprint training session (i.e commonly 5 to 15 repetitions, up to 500m total volume). Respecting these conditions and the preference of athletes, ATD method seemed the more appropriate, allowing the most cycle comparisons in the same time span.

Procedure. For each participants, sixteen repetitions (2 sets of 8) of maximal 30m-sprint are applied, on the same track, either with " carbon super-spikes " (CS) or standard spikes (SS), in random order for each repetition, during a 3h total session a day. Repetitions are preceded by a full warm-up, and followed by a cool-down phase. Rest time between sets and repetitions is standardised (20 and 8-10 minutes).

Block starting can't be choosen in order to limit bias (reaction time, adjustment…) and to allow radar records at the pelvis height (1-m high), as recommended, so that a split-stance starting position was adopted, without any starter (" as soon as ready ").

A path is created between a " polling booth " zone, and the start- and finish lines. In this blinding zone, athletes are sitted on a wheelchair, blindfolded, and putted on with their shoes, which are already covered by dark socks allowing spikes free (athletes' visual blinding). Footwear management by the investigators avoid athletes to have tactile information (athletes'somesthesic blinding). Shoes can not be seen by raters (assessors' visual blinding) or other athletes in that zone. They are then driven to the start-line with the wheelchair, in order to limit gait sensation due to important differences in foams ± air-pods between CS and SS (athletes' proprioceptive blinding). This last point was added after athletes' contribution to the method.

At the start-line, they are asked for their belief between CS or SS, so that a " doubt " rate can be assessed to check for the blind paradigm. Then the blindfold is removed, and the subject stand-up in the starting position.

After the finish-line, a 20m deceleration zone is ended by a wheelchair, where athletes are blindfolded again, shoes tooken off and bringed back to the polling booth zone, as athletes enter the rest zone.

The wind is controlled with the official WA/FFA method and anemometer. The shoes weight is assessed, and standardised, when needed, with the addition of 20g ballasts glued at the heel, so that weight difference is decreased (<50g).

Data are collected and examined by two assessors blinded from the randomisation list.

Subjects. Healthy ≥ 15 years-old athletes presenting with a 750 IAAF/World Athletics points level in sprinting (60-400m), and affiliated to the VAC, are screened with the SIFFA software (Système d'Information-FFA). Fourty-six athletes are eligible, and are contacted by email, as their coaches, for information letter. Due to homogeneity and generalisation concerns, they have to have their own or lended Nike Zoom Maxfly or Victory style. Twenty-five respond positively, and N=21 are availables for one of the half-day-proposed sessions and are included.

Inclusion Criteria:

• Sprinting athletes affiliated to the French Athletic Federation among the Var Athletics Comity
• Sprint Performance > 750pts IAAF/WA (50 to 400m)

Exclusion Criteria:

• Age<15
• Ongoing Injury

Data will be available upon reasonable request. For the Editorial office of the corresponding relevant editor; for meta-analyses needs, or for other detailed requests.

From all types, with de-identified files (Morphometric, cinematic and FVP data, Statistical Analysis, etc..).

Via a controlled access repositories, such as clinicalstudydatarequest.com, the YODA project, or Vivli.

as soon as leading article is published

cf Plan Description

Each participant is self-blinded, but also blinded to other participants ' alternative order