Table 2 Categories and definitions of external load variables and internal training impulse (TRIMP) variables in the included studies

Activity frequency, duration, and distance covered

Standing/walking

Activity of no greater intensity than walking. No distinction was made between different intensities of walking [29,30,31] OR Multidirectional movement performed at 0–1 m∙s⁻¹, when not in a defensive stance [32]. A distinction between standing and walking was made in one study whereby standing was identified as movement performed at < 1 m∙s⁻¹ and walking was identified as movement performed at 1.00–1.81 m∙s⁻¹ [33]

Jogging or low-speed running

Forwards or backwards activity without urgency but at a greater intensity than walking [29,30,31] OR Multidirectional movement performed at 1.1–3.0 m·s⁻¹, when not in a defensive stance [32] OR Forwards or backwards movement at 1.81–2.83 m·s⁻¹ [33]

Running or moderate-speed running

Forwards or backwards activity at an intensity greater than jogging with a moderate degree of urgency, but not approaching an intense level of movement [29,30,31] OR Multidirectional movement performed at 3.1–7.0 m·s⁻¹, when not in a defensive stance [32] OR Forward or backwards movement at 2.83–4.00 m·s⁻¹ [33]

Sprinting or maximal-speed running

Forwards movement at an intensity greater than running, characterized by elongated strides, effort and purpose at or close to maximum [29,30,31] OR Multidirectional movement performed at > 7.0 m·s⁻¹, when not in a defensive stance [32] OR Forward or backwards movement at > 4 m·s⁻¹ [33] or > 5.8 m·s⁻¹ [34]

Low-intensity shuffling or specific movements

Movement without urgency in a sideways or backwards direction using a shuffling action of the feet [29, 30] OR Movement performed strictly in a defensive stance at ≤ 2 m·s⁻¹ [32] OR Any foot action that differed from ordinary walking or running at < 1.67 m·s⁻¹ [31]

Moderate-intensity shuffling or specific movements

Movement at a medium intensity with a moderate degree of urgency in a sideways or backwards direction using a shuffling action of the feet [29, 30] OR Any foot action that differed from ordinary walking or running at 1.67–2.50 m·s⁻¹ [31]

High-intensity shuffling or specific movements

Movement at a high intensity characterized by effort and urgency in a sideways or backwards direction using a shuffling action of the feet [29, 30] OR Multidirectional movement performed strictly in a defensive stance at > 2 m·s⁻¹ [32] OR Any foot action that differed from ordinary walking or running at > 2.5 m·s⁻¹ [31]

Jumping

The time from the initiation of the jump motion until the landing is complete [29, 30] OR Any movement whereby a player initiates a jump and breaks feet contact with the ground [32] OR Any movement which involves jumping from the ground with an impulse involving more than 400 ms of flight time, to land in the same or another place [35] OR Calculated using a proprietary, undisclosed algorithm [36]

Dribble

Movement in which a player is actively in possession of and dribbling the ball [32]

Upper body

Movement that involves raising one or both arms above the horizontal plane at the level of the shoulder [32]

Steps

Movement that implies advancing with a flight time of < 400 ms [35, 37]

Inertial movement analysis (IMA) variables

High-intensity IMA events

The sum of accelerations (− 45° to 45°; where 0° is forward), decelerations (− 135° to 135°), and changes of direction (− 135° to − 45° for left and 45° to 135° for right) at ≥ 3.5 m·s⁻¹ [38, 36]

Accelerometer-derived variables

PlayerLoad™

A proprietary metric sampled at 100 Hz and calculated as the square root of the sum of the squared rate of change in acceleration across the transverse (x), coronal (y), and sagittal (z) planes multiplied by a scaling factor of 0.01 [38, 36]:

\(Player load^{{{\text{TM}}}} = \left[ {\left( {\surd Ac1_{n} - Ac1_{n - 1} } \right)^{2} + \left( {Ac2_{n} - Ac2_{n - 1} } \right)^{2} + \left( {Ac3_{n} - Ac3_{n - 1} )^{2} } \right)} \right] * 0.01\)

Player load

The vectorial magnitude derived from the triaxial accelerometer, sampling at 100 Hz and using the formula [35, 37]:

\(Player load_{t = n} \mathop \sum \limits_{t = 0}^{t = n} \surd (Z_{t = i + 1} - Z_{t = i} )^{2} + (X_{t = i + 1} - X_{t = i} )^{2} + (Y_{t = i + 1} - Y_{t = i} )^{2}\)

OR Derived from the triaxial accelerometer sampling at 100 Hz or ultra-wide band antennae sampling at 20 Hz, and calculated using the formula [34]:

\(Player load_{n} = \surd [(ACx_{n} - Acx_{n - 1} )^{2} + (ACy_{n} - Acy_{n - 1} )^{2} + \left( {ACz_{n} - ACz_{n - 1} )^{2} } \right]/100\)

TRIMP

The product of PlayerLoad™·min⁻¹ and session duration [39]

Average net force (AvF_net)

The three planes of triaxial accelerations are filtered using a dual-pass, fourth-order Butterworth filter (high pass: 0.1 Hz, low pass: 15 Hz). After filtering, the product of the instantaneous acceleration vector and player’s body mass are used to determine instantaneous net force [40, 41]

Internal training impulse (TRIMP) variables

Edwards’ Summated-Heart-Rate-Zones

Multiply the time spent (min) in five different heart rate zones by the corresponding weighting factor for each zone (50–60% HR_max = 1; 60–70% HR_max = 2; 70–80% HR_max = 3; 80–90% HR_max = 4; and 90–100% HR_max = 5), then sum the calculated values [42]

Modified Summated-Heart-Rate-Zones

Multiply the time spent (min) in five different heart rate zones by the corresponding weighting factor for each zone (50–60% HR_peak = 1, 60–70% HR_peak = 2, 70–76% HR_peak = 3, 77–84% HR_peak = 4, and 85–100% HR_peak = 5), then sum the calculated values [43]

OR Multiply the time spent (min) in five different heart rate zones by the corresponding weighting factor for each zone (50–59.9% HR_max = 1, 60–69.9% HR_max = 2, 70–79.9% HR_max = 3, 80–89.9% HR_max = 4, and 90–100% HR_max), then sum the calculated values [44]

Banister’s TRIMP

Banister’s TRIMP = D × (Δ HR ratio) × e^{(b × Δ heart rate ratio)}, where D = session duration (min), e = constant set at 2.718, b = weighting factor set at 1.67 for females, and Δ HR ratio = (average heart rate during exercise − resting heart rate) ÷ (maximal heart rate during exercise − resting heart rate) [45]