10 Feb Responses to Extra-time: Biomechanical and Physiological Approach

Most of the research related to fatigue analyzes the typical 90-min matches. However, many competitions outcomes are decided in extra-time (ET). In fact, at the previous four FIFA World Cups, 36% of knockout phase matches have proceeded to ET with 50% at the 2014 tournament requiring 120 min of match-play. Previous studies have shown a significant increase in fatigue in ET, manifested in a reduction of number of accelerations, decelerations, and number high speed running (HS) performed. Furthermore, higher plasma glycerol, nonesterified fatty acids, and adrenaline as well as lower blood lactate (BLa) and glucose have been observed during ET, which is indicative of an increased rate of lipolysis. This change in energy pathway potentially explains the reductions in HS and sprint performance as evidence suggests that the favorable energy pathway to fuel high-intensity exercise is glycogenolysis. In this sense, authors obtained the respiratory exchange ratio (RER) to estimate substrate utilization may provide practitioners and coaches with novel insight into CHO usage during ET.

“Previous studies have shown a significant increase in fatigue in ET, manifested in a reduction of number of accelerations, decelerations, and number high speed running performed”

A novel metric that has been proposed by Catapult Innovations as a measure of movement efficiency is that of PlayerLoad (PL) (instantaneous rate of acceleration across three planes of motion).

This study aimed to investigate the biome- chanical and physiological responses to 120 min of treadmill-based soccer-specific exercise. A secondary aim was to examine the test–retest reliability of these responses.

Twelve soccer players performed 120 min of soccer-specific exercise. Tri-axial (PLTotal) and uni-axial PlayerLoad in the vertical (PLV), anterior–posterior (PLA–P), and medial–lateral (PLM–L) planes were monitored using a portable accelerometer. Likewise, respiratory exchange ratio (RER) was recorded throughout exercise. At the end of each 15-min period, players provided differential ratings of perceived exertion for legs (RPE-L), breathlessness (RPE-B) and overall (RPE-O), and capillary samples were taken to measure blood lactate (BLa) concentrations. The soccer-specific exercise was completed twice within 7 days to assess reliability.

The results showed that:

• PlayerLoad: higher during E8 (105′-119′) compared to E1 (0′-14′) (+9.9 ± 5.3%; p = 0.002; d = 0.8).
• Physiological and physical responses: RER decreased during E8 (105′-119′)compared to E1 (0′-14′). For RPE-L, a significant increase was detected from E1 to E8 and a similar pattern was evident for RPE-O.

 

Figure 2. This graph shows the time history changes in PLTotal response throughout 120 min of soccer-specific exercise.

Take Home Messages:

1. Finding suggests that the physical capacity of players is reduced during ET matches. However, caution should be applied when interpreting match-play observations as they do not account for contextual variables.
2. In recent years, many matches are decided in the ET. Preparing players for the additional 30- min duration may reduce injury-risk and increase physical performance, ultimately increasing team success.
3. Fat oxidation increases during ET but their RER values during ET (0.87 au) suggest that CHO is still being utilized. In fact, glucose levels were potentially depleted and less was available to undergo biotransformation during ET. Correct fluid restoration plays a crucial role in delaying fatigue.