Methods

Subjects 

This study was performed by eight active athletes (mean \(\frac{+}{ }\) SD, age: 25.5 \(\frac{+}{ }\) 2.9 (range: 22-32) years, weight: 75.1 \(\frac{+}{ }\)7.7 kg, height: 179.9 \(\frac{+}{ }\)3.7 cm; 7 male, 2 female athlete) with various fitness levels. Previous to the test, all subjects performed an 5000-meters all-out trial in order to determine their individual MLSS. All subjects were informed about the purpose, benefits, and risks of the test and volunteered to participate in this study. 

Materials

Each athlete was tested on an outdoor track field (400 meters). The use of audio files with timed signals to a specific speed, as well as cones separated every 25 meters on the track helped the athletes to keep up with their individual pace in every stage. Lactate concentrations were determined from earlobe-sampled capillary blood using Biosen C-Line Clinic. Furthermore, the subjects HR and RPE were taken at rest and after each stage. 

Test Protocol

Stage duration 

The use of 3-minute stages was selected in order to provide enough time to produce representable lactate concentrations, as well as limit the risk of premature exhaustion by lengthening the test.

Blood-Sampling Regimen:

Blood samples were taken at rest and after every stage including the priming and reverse segment within 25-35 seconds, ideally.

Reverse Lactate Threshold Test:

The priming segment of the RLT is used as a gradually increased warm-up in order to elevate lactate concentrations exponentially above the individual MLSS levels. This segment includes four stages, where the last stage represents peak intensity by being five percent higher than the estimated MLSS intensity. The first stage is ten percent and the second stage is 5 percent lower than the MLSS intensity, respectively,  which is used in the third stage. The reverse segment followed immediately after the priming segment consisting of six stages. The intensity was decreased by 0.1 m s-1 in every stage. 

MLSS Estimation:

The MLSS is represented by the highest point of the lactate concentration curve which is decreasing more than 0.2 mmol/L in the following stage and does not show any increase from that point. By using the HR and RPE, the steady state is determined as the intensity at which the athlete´s HR decreased by three beats per minute in the following stage and the athlete´s RPE decreased by one number on the RPE scale.

MLSS Verification:

The MLSS was verified by performing two 30-min MLSS-type testing sessions after five and seven days following the RLT test. MLSS was considered validated if the lactate concentration did not rise over 1.0mmol/L between the 10th and 30th minute of the test. 

Video Analysis

All subjects were filmed each round by using a Canon 550d camera with 50 Hz in order to determine their running performance and food strike pattern. Important parameters included stride length, stride frequency, as well as ground contact time. 

Statistical Analysis

The entire statistical analysis was determined by using Microsoft Excel.

Results