Energy Cost of Continuous Shuttle Running: Comparison of 4 Measurement Methods

Speed Effects on the Accuracy of Heart Rate as Oxygen-Uptake Indicator in Short-Distance Shuttle Running

Purpose: Despite the accuracy of heart rate (HR) as an indicator of the aerobic engagement has been evaluated in several intermittent on-court activities, its validity as an oxygen uptake (V ˙ O 2 ) indicator during shuttle running over short paths remains uncertain. Moreover, it is unclear whether speed may affect such validity. This study evaluated the HR ability in estimating the V ˙ O 2 during 5-m shuttle running at different speeds. Methods: V ˙ O 2 and HR of 12 physically active young men were recorded during an incremental forward running (FW) protocol and a 5-m shuttle test at 50%, 60%, and 75% of maximal aerobic speed (MAS). Slope and intercept of the relationship between HR and V ˙ O 2 (HR/V ˙ O 2 ) were individually determined, in both protocols. The HR measured during the shuttle test was used in the FW HR/V ˙ O 2 to estimate V ˙ O 2 at each shuttle speed. A paired Student's t-test compared slopes and intercepts of the two HR/V ˙ O 2 . A two-way RM-ANOVA and an equality test examined, respectively, the differences and the equality between measured and estimated V ˙ O 2 . Lastly, a Bland-Altman plot described the accuracy and precision of the estimated V ˙ O 2 at each shuttle intensity. Results: Slopes and intercepts of the HR/V ˙ O 2 appeared not different between FW and shuttle running. At 50%MAS, HR underestimated the V ˙ O 2 (~7%), whereas returned accurate values at the two higher velocities, although with high variability (±18%). Conclusions: When using HR as V ˙ O 2 indicator during shuttle running over short paths, a separated analysis of the HR validity as V ˙ O 2 indicator is recommended especially when administering different exercise intensities.

Energetics (and Mechanical Determinants) of Sprint and Shuttle Running

Unsteady locomotion (e. g., sprints and shuttle runs) requires additional metabolic (and mechanical) energy compared to running at constant speed. In addition, sprints or shuttle runs with relevant speed changes (e. g., with large accelerations and/or decelerations) are typically short in duration and, thus, anaerobic energy sources must be taken into account when computing energy expenditure. In sprint running there is an additional problem due to the objective difficulty in separating the acceleration phase from a (necessary and subsequent) deceleration phase.In this review the studies that report data of energy expenditure during sprints and shuttles (estimated or actually calculated) will be summarized and compared. Furthermore, the (mechanical) determinants of metabolic energy expenditure will be discussed, with a focus on the analogies with and differences from the energetics/mechanics of constant-speed linear running.

Comparison of Physiological and Perceptional Responses to 5-m Forward, Forward-Backward, and Lateral Shuttle Running

Purpose

The aim of this study was to investigate the physiological and perceptional responses to forward, forward-backward, and lateral shuttle running.

Methods

Twenty-four eligible male subjects performed a maximal oxygen uptake (VO_2max) test and three directional modes (i.e., forward, forward-backward, and lateral) of 5-m shuttle running at the speed of 6 km⋅h^–1 for 5 min on separate days. Heart rate (HR) and oxygen uptake (VO₂) were continuously measured during the whole tests. Rating of perceived exertion (RPE) was inquired and recorded immediately after the test. Capillary blood samples were collected from the earlobe during the recovery to determine the peak value of blood lactate concentration ([La^–]_peak).

Results

Running directional mode had significant effects on HR (F = 72.761, P < 0.001, η²_p = 0.760), %HR_max (F = 75.896, P < 0.001, η²_p = 0.767), VO₂ (F = 110.320, P < 0.001, η²_p = 0.827), %VO_2max (F = 108.883, P < 0.001, η²_p = 0.826), [La^–]_peak (F = 55.529, P < 0.001, η²_p = 0.707), and RPE (F = 26.268, P < 0.001, η²_p = 0.533). All variables were significantly different between conditions (P ≤ 0.026), with the variables highest in lateral shuttle running and lowest in forward shuttle running. The effect sizes indicated large magnitude in the differences of all variables between conditions (ES = 0.86–2.83, large) except the difference of RPE between forward and forward-backward shuttle running (ES = 0.62, moderate).

Conclusion

These findings suggest that the physiological and perceptional responses in shuttle running at the same speed depend on the directional mode, with the responses highest in lateral shuttle running, and lowest in forward shuttle running.

Fatigue Induced by Repeated Changes of Direction in Élite Female Football (Soccer) Players: Impact on Lower Limb Biomechanics and Implications for ACL Injury Prevention

Background

The etiology of Anterior Cruciate Ligament (ACL) injury in women football results from the interaction of several extrinsic and intrinsic risk factors. Extrinsic factors change dynamically, also due to fatigue. However, existing biomechanical findings concerning the impact of fatigue on the risk of ACL injuries remains inconsistent. We hypothesized that fatigue induced by acute workload in short and intense game periods, might in either of two ways: by pushing lower limbs mechanics toward a pattern close to injury mechanism, or alternatively by inducing opposed protective compensatory adjustments.

Aim

In this study, we aimed at assessing the extent to which fatigue impact on joints kinematics and kinetics while performing repeated changes of direction (CoDs) in the light of the ACL risk factors.

Methods

This was an observational, cross-sectional associative study. Twenty female players (age: 20-31 years, 1st-2nd Italian division) performed a continuous shuttle run test (5-m) involving repeated 180°-CoDs until exhaustion. During the whole test, 3D kinematics and ground reaction forces were used to compute lower limb joints angles and internal moments. Measures of exercise internal load were: peak post-exercise blood lactate concentration, heart rate (HR) and perceived exertion. Continuous linear correlations between kinematics/kinetics waveforms (during the ground contact phase of the pivoting limb) and the number of consecutive CoD were computed during the exercise using a Statistical Parametric Mapping (SPM) approach.

Results

The test lasted 153 ± 72 s, with a rate of 14 ± 2 CoDs/min. Participants reached 95% of maximum HR and a peak lactate concentration of 11.2 ± 2.8 mmol/L. Exercise duration was inversely related to lactate concentration (r = -0.517, p < 0.01), while neither%HR _max nor [La^-] _b nor RPE were correlated with test duration before exhaustion (p > 0.05). Alterations in lower limb kinematics were found in 100%, and in lower limb kinetics in 85% of the players. The most common kinematic pattern was a concurrent progressive reduction in hip and knee flexion angle at initial contact (10 players); 5 of them also showed a significantly more adducted hip. Knee extension moment decreased in 8, knee valgus moment increased in 5 players. A subset of participants showed a drift of pivoting limb kinematics that matches the known ACL injury mechanism; other players displayed less definite or even opposed behaviors.

Discussion

Players exhibited different strategies to cope with repeated CoDs, ranging from protective to potentially dangerous behaviors. While the latter was not a univocal effect, it reinforces the importance of individual biomechanical assessment when coping with fatigue.

Metabolic Demands, Center of Mass Movement and Fractional Utilization of V ˙ O 2 max in Elite Adolescent Tennis Players During On-Court Drills

The aim of the study was to investigate the exercise intensity and energy expenditure during four types of on-court tennis drills. Five female and five male tennis players participated in the study (age: 17 ± 2 years; V∙O2max: 54 ± 6 ml·kg⁻¹·min⁻¹). Anthropometric measures were taken for each player and, on separate days, each player performed (i) treadmill running to determine V∙O2max and (ii) four different tennis drills (Drill1-4) during which V∙O2, blood lactate concentration, ratings of perceived exertion (RPE 6–20), and displacement of center of mass (m) using 3D kinematics were recorded. The drills were designed to simulate match play with 90 s of rest between each drill. A repeated two-way ANOVA was used for physiological and biomechanical data and Friedman's test for RPE using < α 0.05. Fractional utilization of V∙O2max was greatest during Drill1 81.8 ± 7.0% and lowest during Drill4 72.4 ± 5.2% (p < 0.001) with no difference between sexes (p > 0.05). The highest energy expenditure was during Drill1 and lowest during Drill4 (77 ± 15 and 49 ± 11 kcal, respectively, p < 0.05). Energy expenditure per meter for Drill1–Drill4 was subsequently reduced for each drill with 10.5 ± 2.1, 9.9 ± 2.2, 7.6 ± 1.7, and 8.0 ± 1.6 J·kg⁻¹·m⁻¹ (p < 0.01). There were no interaction effects for any of these variables. RPE (6–20) and blood lactate concentration post Drill1–Drill4 were 17.5, 15.5, and 13.0 (overall, legs and arms, p < 0.001) and 5.9 ± 2.0, 4.9 ± 1.9, 5.6 ± 2.0, and 5.0 ± 2.2 mmol·l⁻¹ (p < 0.05). The findings of this study demonstrate that the on-court tennis drills performed here are suitable for high intensity training in junior tennis players. The energy expenditure per minute is comparable to similar sports whereas the energy expenditure per meter is notably greater.

Use of Machine Learning and Wearable Sensors to Predict Energetics and Kinematics of Cutting Maneuvers

Changes of directions and cutting maneuvers, including 180-degree turns, are common locomotor actions in team sports, implying high mechanical load. While the mechanics and neurophysiology of turns have been extensively studied in laboratory conditions, modern inertial measurement units allow us to monitor athletes directly on the field. In this study, we applied four supervised machine learning techniques (linear regression, support vector regression/machine, boosted decision trees and artificial neural networks) to predict turn direction, speed (before/after turn) and the related positive/negative mechanical work. Reference values were computed using an optical motion capture system. We collected data from 13 elite female soccer players performing a shuttle run test, wearing a six-axes inertial sensor at the pelvis level. A set of 18 features (predictors) were obtained from accelerometers, gyroscopes and barometer readings. Turn direction classification returned good results (accuracy > 98.4%) with all methods. Support vector regression and neural networks obtained the best performance in the estimation of positive/negative mechanical work (coefficient of determination R² = 0.42-0.43, mean absolute error = 1.14-1.41 J) and running speed before/after the turns (R² = 0.66-0.69, mean absolute error = 0.15-018 m/s). Although models can be extended to different angles, we showed that meaningful information on turn kinematics and energetics can be obtained from inertial units with a data-driven approach.

Kinematic effects of repeated turns while running

In team sports, non-contact ACL and MCL injuries occur during abrupt changes of direction, like turns or cutting manoeuvres. Fatigue affects dynamic neuromuscular control and increases knee injury risk. This study analysed how lower limb joints and centre-of-mass kinematics are affected throughout a high-intensity running protocol involving repeated 180°-turns. Twenty young men (18-23 years, BMI: 20.8-24.4 kg m^-2) completed a 5-m shuttle running trial lasting 5 min at an average speed of 75% of their maximum aerobic speed. During the test, cardio-metabolic parameters were obtained, together with joints and centre-of-mass kinematics, using a motion capture system. Kinematic data were compared between the first and the last minute of exercise. Perceived exercise intensity ranged from "hard" to "maximum exertion" and post-exercise lactate concentration ranged from 5.4 to 15.5 mM. The repetition of 180°-turns induced a substantial reduction of hip (-60%, p < .001, large effect) and knee flexion (-40%, p = .003, medium-to-large effect), and an increase of hip adduction and internal rotation (+25-30%, p < .05, medium-to-large effect). Since such movements are factors increasing the likelihood of non-contact knee injuries, we concluded that the prolonged repetition of turns may expose participants to increased risk of ligament failure. Prevention programmes should include discipline-specific neuromuscular training especially in late practices.

Kinematic algorithm to determine the energy cost of running with changes of direction

Changes of direction (CoDs) have a high metabolic and mechanical impact in field and court team sports, but the estimation of the associated workload is still inaccurate. This study aims at validating an algorithm based on kinematic data to estimate the energy cost of running with frequent 180°-CoDs. Twenty-six physically active male subjects (22.4 ± 3.2 years) participated in two sessions: (1) maximum oxygen uptake (V̇O_2,max) and maximal aerobic speed (MAS) test; (2) 5-m continuous shuttle run (two 5-min trials at 50% and 75% MAS, 6-min recovery). In (2), full-body 3D-kinematics and V̇O₂ were simultaneously recorded. Actual cost of shuttle running (C_meas) was obtained from the aerobic, anaerobic alactic and lactic components. The proposed algorithm detects "braking phases", periods of mostly negative (eccentric) work occurring at concurrent knee flexion and ground contact, and estimates energy cost (C_est) considering negative mechanical work in braking phases, and positive elsewhere. At the speed of, respectively, 1.54 ± 0.17 and 1.90 ± 0.15 m s^-1 (rate of perceived exertion: 9.1 ± 1.8 and 15.8 ± 1.9), C_meas was 8.06 ± 0.49 and 9.04 ± 0.73 J kg^-1 m^-1. C_est was more accurate than regression models found in literature (p < 0.01), and not significantly different from C_meas (p > 0.05; average error: 8.3%, root-mean-square error: 0.86 J kg^-1 m^-1). The proposed algorithm improved existing techniques based on CoM kinematics, integrating data of ground contacts and joint angles that allowed to separate propulsive from braking phases. This work constitutes the basis to extend the model from the laboratory to the field, providing a reliable measure of training and matches workload.