1. 1. Department of Kinesiology, University of Alabama, Tuscaloosa, AL
DAILY AND CHRONIC HRV RESPONSES TO TRAINING IN ELITE FOOTBALL PLAYERS DURING SPRING CAMP
Andrew A. Flatt1,2, Michael R. Esco1, Jeff R. Allen1, James B. Robinson1, Ryan L. Earley1, Jonathan E. Wingo1, Michael V. Fedewa1, Clay M. Keith1
1. Department of Kinesiology, University of Alabama, Tuscaloosa, AL
2. Department of Health Sciences, Armstrong State University, Savannah, GA
Abstract
Methods
Results
Vagally-mediated heart rate variability (lnRMSSD) reflects cardiac-parasympathetic modulation and is commonly used as recovery status marker among athletes. Fitness level, body mass and physiological responses to training vary among positional groups in football. Thus, we hypothesize that lnRMSSD responses to training may also differ among positions. However, daily nor chronic lnRMSSD responses to training among football players have previously been investigated. PURPOSE: To evaluate daily lnRMSSD responses to training among positional groups from an elite college football team during Spring training camp. Additionally, relationships between chronic (i.e., 4-week) lnRMSSD trends and microsensor-derived training load values (PlayerLoad) were quantified. METHODS: Baseline lnRMSSD (lnRMSSD_BL) was compared with lnRMSSD acquired ~20 h following a football practice (lnRMSSDpost20) among positional groups comprised of backs and receivers (SKILL; n = 11), running backs, linebackers and tight-ends (MID-SKILL; n = 9) and linemen (LINEMEN n = 5) with a linear mixed model and effect sizes (ES). Pearson’s r was used to evaluate the relationship between changes in lnRMSSD from lnRMSSD_BL to lnRMSSDpost20 (ΔlnRMSSD) and body mass. Pearson and partial correlations were used to quantify relationships between chronic mean and coefficient of variation (CV) of lnRMSSD (lnRMSSD_chronic and lnRMSSDcv, respectively) with the mean and CV of PlayerLoad (PL_chronic and PL_cv, respectively) and body mass. RESULTS: A significant position x time interaction was observed for lnRMSSD (F2,22 = 5.46, p = 0.012). lnRMSSD_BL was significantly greater than lnRMSSDpost20 for LINEMEN (p <0.01; ES = -1.24, Large) while differences for SKILL (p = 0.998; ES = -0.10, Trivial) and MID-SKILL (p = 0.343; ES = -0.50, Small) were not statistically significant. ΔlnRMSSD was significantly related to body mass (r = -0.62, p <0.01, Large). lnRMSSDcv was significantly related to body mass (r = 0.48, p = 0.02, Moderate) and PL_chronic (r = -0.60, p <0.01, Large). After adjusting for body mass, lnRMSSDcv and PL_chronic remained significantly related (r = -0.43, p <0.05, Moderate). CONCLUSIONS: ~20 hours following a football practice, lnRMSSD values were suppressed for LINEMEN while SKILL and MID-SKILL values returned to near or within baseline levels. Athletes with greater body mass showed the largest reductions in lnRMSSD. Greater daily perturbations in lnRMSSD throughout Spring training camp (i.e., lnRMSSDcv) were associated with lower PL_chronic, independent of body mass. PRACTICAL APPLICATIONS: lnRMSSD responses to training vary among football positional groups and are largely related to body mass. ~20 hours of rest between training sessions does not appear adequate for complete cardiac-parasympathetic recovery among LINEMEN. Training load values are commonly used to indirectly assess training capacity among athletes. As such, we interpret the inverse relationship between daily perturbations in lnRMSSD (i.e., lnRMSSDcv) and PL_chronic to indicate that aerobic fitness is likely a major contributor to the differential lnRMSSD responses to training among positions. However, further research is needed to support this postulation. Standardized, sixty-second lnRMSSD acquired via mobile devices under resting conditions at the training facility may provide meaningful information regarding training responses among elite college football players.
25 players (n = 11 SKILL, 9 MID-SKILL and 5 LINEMEN) from a D-1 team were monitored throughout a 4-week Spring camp (14 training sessions). Vagally-mediated HRV (lnRMSSD) recordings were acquired ~90 min before each practice at the training facility via tablet and finger-pulse plethysmography (depicted below). PlayerLoad was quantified via triaxial accelerometers for each session.
Table 1. Model effects and lnRMSSD values among and between positional groups and across time.
* p < 0.05 vs. SKILL; ¥ p < 0.05 vs. BL across all groups; € p < 0.05 vs. BL for LINEMEN.
Figure 2. Scatterplots displaying a) lnRMSSDcv and body mass and b) lnRMSSDcv and PL_chronic.
Model effect F df P
Mean ± SD lnRMSSD
Position
4.24
2, 22
0.028
SKILL: 82.4 ± 7.6
MID-SKILL: 76.4 ± 8.0
LINEMAN: 71.0 ± 10.3*
Time
18.47
1, 22
<0.001
BL: 80.0 ± 7.3
POST: 76.0 ± 10.7¥
Position × Time
5.46
0.012
SKILL BL: 82.8 ± 7.2
SKILL Post: 82.0 ± 8.3
MID-SKILL BL: 78.4 ± 6.2
MID-SKILL Post: 74.4 ± 9.5
LINEMAN BL: 76.6 ± 8.6
LINEMAN Post: 65.4 ± 9.5€
The lnRMSSD from Monday, Wednesday and Friday of Week 2 represented baseline (lnRMSSD_BL) as each of these training sessions were separated by ≥ 44 h. Saturday of the same week represented lnRMSSDpost20 as it was preceded by only ~20 h rest before the next session.
lnRMSSD_BL was compared with lnRMSSDpost20 among positional groups with a linear mixed model and effect sizes (ES). Pearson’s r was used to evaluate the relationship between changes in lnRMSSD from lnRMSSD_BL to lnRMSSDpost20 (ΔlnRMSSD) and body mass. Pearson and partial correlations were used to quantify relationships between chronic mean and CV of lnRMSSD (lnRMSSD_chronic and lnRMSSDcv, respectively) with the mean and CV of PlayerLoad (PL_chronic and PL_cv, respectively) and body mass.
Results
A position × time interaction was observed for lnRMSSD (Table 1). Large (ES = -1.24), moderate (ES = 0.50) and trivial (ES = -0.10) reductions in lnRMSSD_post20 were observed for LINEMEN, MID-SKILL and SKILL, respectively. Individual and group responses are displayed in Figure 1a. Players with greater body mass experienced larger reductions in lnRMSSDpost20 (Figure 1b.)
Introduction
Conclusions & Practical Applications
Figure 1. a) Individual and group lnRMSSD responses to training and b) scatterplot representing the relationship between ΔlnRMSSD and body mass. ). Horizontal dashed lines represent ± 0.5 of BL coefficient of variation (i.e., smallest worthwhile change).
lnRMSSDcv was significantly related to body mass (Moderate) and PL_chronic (Large) (Figure 2a). After adjusting for body mass, lnRMSSDcv and PL_chronic remained significantly related (r = -0.43, p <0.05, Moderate).
Despite a demanding training schedule and high injury rate in American football (AF), research pertaining to training status monitoring among AF players is limited. Body mass and physical training demands vary by position, thus daily recovery status markers may also differ by position.
HRV reflects autonomic modulation of the heart and can be measured non-invasively with smartphone app’s. Vagally-mediated HRV is considered a global marker of homeostasis and reflects cardiovascular recovery following a training session. HRV responses to AF training have not been investigated.
Greater daily fluctuation in HRV is associated with lower aerobic fitness. Thus, AF players who perform greater chronic (i.e., 4-week) workloads may display less daily fluctuation in HRV and vice-versa.
The purpose of this study was to evaluate the daily HRV response to AF training among elite college players. A secondary aim was to assess relationships between chronic workloads and chronic HRV trends (i.e., mean and CV) from an annual Spring training camp.
At ~20 h post-training, lnRMSSD values were suppressed for LINEMEN while SKILL and MID-SKILL values returned to near or within baseline. Therefore, LINEMEN may be more susceptible to autonomic nervous system imbalance during more intensive training periods. However, whether unrecovered lnRMSSD affects acute performance or injury-risk requires further investigation.
We speculate that lower aerobic fitness, larger body mass, greater reliance on anaerobic-glycolytic metabolism during training and disturbed fluid balance may all have contributed to the incomplete cardiac-parasympathetic recovery in LINEMEN between consecutive-day training sessions.
A capacity for greater chronic workloads may be protective against daily perturbations in cardiac-autonomic homeostasis based on the inverse relationship between PL_chronic and lnRMSSDcv, independent of body mass.
Standardized, 60-s lnRMSSD via mobile devices at the training facility may provide meaningful information regarding training responses among AF players.