Participants
Eight female (age: 21.6 ± 2.8yrs, height: 161 ± 4 cm, weight: 60.3 ± 6.8 kg, ~ 8 h training per week) and nine male (age: 23.2 ± 2.5yrs, height: 175.2 ± 7 cm, weight: 71.3 ± 6.7 kg, ~ 8 h training per week) sub-elite gymnasts of the University`s artistic gymnastics team participated in the study. All athletes were free from any medical issues and were informed about reasons and risks of the measurements. All subjects signed informed consent, the study was approved by the institutional ethics committee of the Philipps-University Marburg (AZ-3-12-18) and carried out in accordance with the standards of ethics outlined in the Declaration of Helsinki.
Procedure
All participants took part in a floor competition (FC) with metabolic measurements in a gym. The floor competition which was conducted on an official artistic gymnastics floor (Spieth Gymnastics GmbH, Altbach, Germany) was carried out like an official competition to mimic realistic conditions as much as possible. Due to the measurements, i.e., breath-by-breath spirometry it was not possible to conduct the experiment during an official competition. The routine for the FC was developed by the gymnastics team coach with assistance of an experienced athlete and the laboratory manager in order to ensure an officially valid but also secure routine for athletes and equipment. Finally, the developed routine was overseen and approved by an experienced, official judge of the Bavarian Gymnastics Federation. The only modification compared to a regular floor competition concerned the difficulty of the artistic elements: As each athlete normally performs an individual exercise with elements appropriate to his or her ability, the exercise difficulty was reduced in a standardized manner. Both exercise difficulty and the standardized reduction in difficulty were applied as laid down in international competition rules of the “Code de Pointage” (CdP)(FIG, Lausanne, Switzerland) [2, 3]. Prior to the test, all athletes were given the chance to train for the FC routine for an appropriate amount of time during the team training and to accommodate to wearing the spirometry equipment during the routine. On the day of the simulated FC all athletes competed in a randomized order and under similar conditions as in a regular competition. All subjects prepared by themselves and used their individual pre-competition warm-up routine. Then, the subjects were precisely instructed to the test protocol, again. In order to calculate the metabolic profile for each athlete using the PCr-LA-O2 method [15] oxygen consumption (VO2) was continuously measured during the FC and until 15 min post-exercise using a portable breath-by-breath metabolic cart (Metamax 3B, Cortex Biophysik GmbH, Leipzig, Germany). The metabolic cart was calibrated before being attached to each athlete. From pre-tests we knew that data quality may be impaired by very hard impact forces during landing and by restricted breathing patterns. Therefore, two researchers independently checked the raw VO2 data for unphysiological breath-by-breath variations. In three cases high shock levels resulted in unphysiological bumps in the VO2 curve. In these cases (1 male, 2 female) the measurements were carried out again two days later. Moreover, before, immediately after the test and 1, 2, 3, 4, 5 and 7 min post-test [16], 20µL capillary blood were collected from the hyperemic ear lobe for enzymatic-amperometric blood lactate concentration determination (Biosen C-line, EKF-Diagnostik, Eppendorf, Germany). Additionally, HR was obtained continuously via a portable HR monitor (H10; Polar Electro Oy, Kempele, Finland). All athletes were filmed during their floor routine and the execution was independently evaluated by two official judges who strictly followed the international rules of the “Code de Pointage” (CdP) [2, 3]. The final score of FC was calculated as: final score = difficulty score + execution score, with difficulty score being predefined according to the CdP and execution score equaling 10,00—average withdrawal from the two judges.
In addition to the simulated competition, jumping ability and anaerobic power were assessed by a standardized drop-jump test from 45 cm height (DJ), a counter-movement jump (CMJ) [17] and a 30 s Bosco-Continuous-Jumping-Test (CJ30) [18]. For the DJ subjects were instructed to jump as high as possible while keeping the ground contact time as short as possible and the CJ30 was carried out exactly as described in the original study [18]. The jump tests were conducted three days apart from the simulated floor competition at a comparable time of the day to ensure that all athletes would be free from fatigue or delayed onset of muscle soreness. Again, all athletes were familiarized with the test procedures and the test order was assigned randomly. Before the jump tests a standardized warm-up protocol was performed to prepare the athletes for high intensity activity. During the warm-up intense movements did not last longer than 3 s, in order to avoid blood lactate concentration accumulation [19]. Ground contact time and flight time were measured for DJ, CMJ and CJ30 with photoelectric cell technology (Optojump Next, Microgate, Bolzano, Italy). Jump height (in cm) and jump power (in W∙kg−1) were calculated based on these values by the Optojump software, which can be considered a valid procedure [20]. Peak and mean power (in W∙kg−1) for CJ30 were calculated as described in Bosco, Luhtanen [18]. Additionally, before, immediately after CJ30, as well as 1, 2, 3, 4, 5 and 7 min post-test [16], 20µL capillary blood were collected from the hyperemic ear to assure determination of peak blood lactate concentration (BLCpeak in mmol∙l−1; Biosen C-line, EKF-Diagnostik, Eppendorf, Germany).
Calculation of the Metabolic Profiles
The individual metabolic profiles for WAG and MAG were calculated using the PCr-LA-O2 method [15]. Consequently, metabolic energy (Wtot) was calculated as the sum of the absolute aerobic (WAER), anaerobic lactic (WBLC) and anaerobic alactic (WPCr) shares:
$$W_{{{\text{tot}}}} = W_{{{\text{AER}}}} + W_{{{\text{BLC}}}} + W_{{{\text{PCr}}}}$$
and metabolic power (Ptot) as Wtot divided by exercise duration:
$$P_{{{\text{tot}}}} = W_{{{\text{tot}}}} \div t$$
All energy shares were calculated in J∙kg−1 and are presented in absolute (J∙kg−1) and relative (% of Wtot) numbers. WAER in J∙kg−1 was calculated from VO2 above rest during FC, caloric equivalent, and body mass by using:
$$W_{{{\text{AER}}}} \left( {{\text{J}}\;{\text{kg}}^{ - 1} } \right) = {\text{VO}}_{2} \left( {{\text{ml}}\,{\text{kg}}^{ - 1} } \right) \cdot {\text{caloric}}\,{\text{equivalent}} \left( {{\text{J}}\,{\text{ml}}^{ - 1} } \right)$$
Since measurement of the resting VO2 before the tests may be difficult due to sympathetic arousal, the equivalent of VO2 in a standing position (4.5 ml∙kg−1∙min−1) was defined as the resting VO2 [21]. Due to increased muscle mass and lower body fat percentage when compared to female non-gymnasts of the same age [22, 23] this value was also applied for the modeling of the metabolic profiles in WAG. Accordingly, VO2 above rest during FC was calculated as the area under the curve of actual VO2 minus 4.5 ml∙kg−1∙min−1. Anaerobic lactic energy (WBLC) was determined from the highest change in blood lactate concentration (Net-BLC) and body mass by using:
$$W_{{{\text{BLC}}}} \left( {{\text{J}}\;{\text{kg}}^{ - 1} } \right) = \Delta BLC \left( {{\text{mmol}}\;{\text{l}}^{ - 1} } \right) \cdot O_{2} - {\text{lactate}}\,{\text{equivalent}} \left( {{\text{ml}}\;{\text{kg}}^{ - 1} \;{\text{mmol}}^{ - 1} \;l} \right) \cdot {\text{caloric}}\,{\text{equivalent}} \left( {{\text{J}}\,{\text{ml}}^{ - 1} } \right)$$
Assuming a distribution space of lactate close to 45% of the body mass, the O2-lactate equivalent is 3.0 ml∙kg−1∙mmol−1∙l [24]. A value of 20.9 J∙ml−1 was employed as caloric equivalent [11]. WPCr was estimated based on the fast component of post-exercise oxygen uptake (VO2PCr) calculated from the latter and body mass by:
$$W_{{{\text{PCr}}}} \left( {{\text{J}}\,{\text{kg}}^{ - 1} } \right) = {\text{VO}}_{{{\text{2PCr}}}} \left( {{\text{ml}}\,{\text{kg}}^{ - 1} } \right) \cdot {\text{caloric}}\,{\text{equivalent}} \left( {{\text{J}}\,{\text{ml}}^{ - 1} } \right)$$
Due to the high exercise intensity a bi-exponential model:
$${\text{VO}}_{{{\text{2EPOC}}}} \left( {{\text{ml}}\,{\text{kg}}^{ - 1} } \right) = a \cdot e^{{\left( { - t \div \tau a} \right)}} + b \cdot e^{{\left( { - t \div \tau b} \right)}} + c$$
was used to fit the fast component of the post exercise oxygen uptake [15]. Then VO2PCr (ml∙kg−1) was derived from the integral of the fast component using:
$${\text{VO}}_{{{\text{2PCr}}}} = a \cdot e^{{\left( { - t \div \tau a} \right)}}$$
To secure a high precision of our model the goodness-of-fit for the curve fitting process had to be r2 > 0.95.
Statistical Analysis
Data-processing procedures and statistics were computed using SPSS 26 (IBM, Chicago, IL) and Origin 2019b (OriginLab, Northampton, MA). Kolmogorov–Smirnov testing and the Levene statistics for homoscedasticity were used to verify the normality of distribution. Differences in energy system contribution between WAG and MAG were tested using a two-way ANOVA (sex × energy system) with repeated measures on the second factor and Bonferroni post-hoc testing. Since FC time was significantly different an additional analysis of covariance was carried out with exercise time as a covariant. Additionally, a one-way ANOVA with repeated measurements was carried out to determine differences between energy systems within WAG and MAG. Differences between performance variables of WAG and MAG were tested by t-tests for independent samples. Statistical correlations between variables are indicated by Pearson’s r. All statistical tests were deemed to be significant at p ≤ 0.05 and effect sizes are shown as Cohen`s d and results are presented as means plus minus standard deviation and 90% confidence intervals (CI).