Reliability of measurements during countermovement jump assessments: Analysis of performance across subphases

Figures & data

Figure 1. Vertical ground reaction force of one CMJ trial and phases determined by jump initiation (F_START), take-off (TO) and landing

Figure 2. Performance measurements derived from vertical ground reaction force during the contact phase. Key inflection points indicate the minimum force (F_MIN), the minimum velocity (V_MIN) and the maximal downward amplitude (D_MAX). Peak force (PF), peak power (PP), and peak velocity (PV) indicate the maximum values registered in a given curve, minimum power (P_MIN) is the lowest value (peak negative value) of the power-time curve and (V_PP) is the velocity achieved at the point where PP occurred. Power and displacement scales have been omitted

Figure 3. Different approaches to determine countermovement jump sub-phases based on: (a) force-time curve, where minimum force delimits the decreasing force time (TF_DEC) and the increasing force time (TF_INC), (b) displacement- or power-time curves, where the downward displacement time (TD_DEC) is measured, (c) velocity-time curve, where F_BRAKE is the point in the force curve at minimum velocity, F_PROP is the point in the force where velocity turns into positive values and T_BRAKE-PF is the time from the initiation of the braking sub-phase to peak force, and (d) force- and displacement-curve

Figure 4. Determination of the transition sub-phase that represents the zone included between the first and second inflection points

Table 1. Contact phase variables, abbreviations, and descriptions

Variable	Abbreviation	Description
Contact Time	TCONTACT	Time from jump initiation to take off
Time to Peak Force	TTPF	Time from jump initiation to the point of peak force
Time to Peak Power	TTPP	Time from jump initiation to the point of peak power
Peak Force	PF	Highest force value registered during the contact phase
Relative Peak Force	rPF	PF divided by mass
Mean Force	MFJUMP	Average force during the contact phase
Relative Mean Force	rMFJUMP	MFJUMP divided by mass
Peak power	PP	Highest power value during the contact phase
Relative Peak Power	rPP	PP divided by mass
Mean Power	MPJUMP	Average of power absolute values during the contact phase
Relative Mean Power	rMPJUMP	MPJUMP divided by mass
Peak Velocity	PV	Highest velocity achieved during the contact phase
Mean Velocity	VJUMP	Average of absolute velocity during the contact phase
Velocity at Peak Power	VPP	Velocity achieved at the point where PP occurred
Maximum Rate of Force Development	RFDMAX	Largest force increased during a 30-ms epoch
Net Impulse	NIJUMP	Sum of the positive net impulse values during the jump
Relative Net Impulse	rNIJUMP	NI JUMP divided by mass

Figure 5. Ratios of force development of the unloading sub-phase (RFD_UNLOAD), the loading sub-phase (RFD_LOAD), the transition sub-phase (RFD_TRANSITION), the braking sub-phase (RFD_BRAKE), and the ratio of force development from the initiation of the braking sub-phase to peak force (RFD_BRAKE-PF)

Table 2. Key Points: data description, mean differences between sessions, and reliability of measures

Variable	Unit	Mean	SD	p	ICC	95% CI	SEM	MD	SWC	%CV
Weight	N	645	70	.959	.998	(.997–999)	3	9	14	10.9
Mass	kg	65.8	7.2	.953	.998	(.997—.999)	0.3	0.9	1.4	10.9
FSTART	N	634	69	.922	.996	(.994—.998)	4	12	14	10.9
FMIN	N	315	126	.040*	.903	(.839—.943)	39	109	25	40.0
PMIN	W	−837	307	.116	.944	(.909—.967)	73	201	61	36.6
VMIN	m·s^−1	−1.06	0.27	.027*	.924	(.873—.955)	0.07	0.21	0.05	25.4
FBRAKE	N	648	71	.962	.998	(.996—.999)	3	9	14	10.9
DMAX	m	0.36	0.07	.805	.903	(.845—.942)	0.02	0.06	0.01	20.8
FPROP	N	1292	270	.784	.900	(.838—.939)	85	237	54	20.9

ICC = intraclass correlation coefficient; 95% CI = 95% confidence interval; SEM = standard error of measurement; MD = minimum difference to be considered real; SWC = smallest worthwhile change; %CV = percentage coefficient of variation; F_START = force at jump initiation; F_MIN = minimum force; P_MIN = minimum power; V_MIN = minimum velocity; F_BRAKE = force at minimum velocity; D_MAX = maximal downward amplitude; F_PROP = force at 0 velocity.

* denotes significant differences from session 1 (p > 0.05).

Table 3. Flight phase

Variables	Units	Mean	SD	p	ICC	95% CI	SEM	MD	SWC	CV%
TFLIGHT	s	0.511	0.036	.957	.934	(.894—.960)	0.009	0.026	0.007	7.1
JH	m	0.32	0.04	.965	.932	(.892—.959)	0.01	0.03	0.00	13.9
RSITIME	s·s^−1	0.53	0.08	.506	.852	(.764—.911)	0.03	0.09	0.02	15.4
RSIHEIGHT	s·s^−1	0.33	0.07	.736	.884	(.815—.931)	0.02	0.06	0.01	19.5
TFLIGHT:TPROP	s·s^−1	1.67	0.26	.434	.857	(.770—.914)	0.098	0.271	0.052	15.4

ICC = intraclass correlation coefficient; 95% CI = 95% confidence interval; SEM = standard error of measurement; MD = minimum difference to be considered real; SWC = smallest worthwhile change; %CV = percentage coefficient of variation; T_FLIGHT = flight phase duration; JH = jump height; RSI_TIME = reactive strength index based on time; RSI_HEIGHT = reactive strength index based on height; T_FLIGHT:T_PROP = ratio of flight time and propulsive time.

Table 4. Contact phase

Variable	Unit	Mean	SD	p	ICC	95% CI	SEM	MD	SWC	CV%
TCONTACT	s	0.977	0.139	.146	.809	(.693—.885)	0.061	0.168	0.028	14.2
TTPF	s	0.807	0.181	.185	.704	(.526—.823)	0.098	0.273	0.036	22.4
TTPP	s	0.912	0.138	.124	.806	(.689—.884)	0.061	0.169	0.028	15.1
PF	N	1472	201	.798	.944	(.910—.966)	48	132	40	13.7
rPF	N·kg^−1	22.4	2.0	.772	.847	(.753—.908)	0.8	2.2	0.4	8.9
MFJUMP	N	813	89	.870	.987	(.979—.992)	10	28	18	10.9
rMFJUMP	N·kg^−1	12.4	0.4	.577	.822	(.714—.893)	0.2	0.5	0.1	3.3
PP	W	3187	505	.959	.974	(.959—.985)	81	226	101	15.8
rPP	W·kg^−1	48.4	4.8	.989	.929	(.886—.957)	1.3	3.5	1.0	9.9
MPJUMP	│W│	752	161	.292	.942	(.907—.965)	39	108	32	21.5
rMPJUMP	│ W·kg^−1│	11.4	1.9	.193	.902	(.843–941)	0.6	1.7	0.4	16.9
PV	m·s^−1	2.61	0.17	.872	.901	(.842—.941)	0.054	0.150	0.034	6.6
VJUMP	│ m·s^−1│	0.83	0.15	.325	.908	(.853—.945)	0.045	0.125	0.030	17.9
VPP	m·s^−1	2.37	0.17	.925	.935	(.896—.961)	0.045	0.123	0.035	7.4
RFDMAX	N·s^−1	6139	2564	.952	.715	(.542—.830)	1369	3794	513	41.8
NIJUMP	N·s	232	40	.378	.977	(.961—.986)	6	17	8	17.1
rNIJUMP	N·s·kg^−1	3.52	0.37	.145	.935	(.893—.962)	0.09	0.26	0.07	10.5

ICC = intraclass correlation coefficient; 95% CI = 95% confidence interval; SEM = standard error of measurement; MD = minimum difference to be considered real; SWC = smallest worthwhile change; %CV = percentage coefficient of variation; T_CONTACT = contact phase duration; TTPF = time to peak force; TTPP = time to peak power; PF = peak force; rPF = relative peak force; MF_JUMP = mean force of the contact phase; rMF_JUMP = relative mean force of the contact phase; PP = peak power; rPP = relative peak power; MP_JUMP = mean power of the contact phase; rMP_JUMP = relative mean force of the contact phase; PV = peak velocity; V_JUMP = mean velocity of the jump; V_PP = velocity at peak power; RFD_MAX = maximum rate of force development; NI_JUMP = net impulse; rNI_JUMP = relative net impulse. │unit│ indicates units are expressed in converted values.

Table 5. Propulsive sub-phase

Variables	Units	Mean	SD	p	ICC	95% CI	SEM	MD	SWC	CV%
TPROP	s	0.311	0.047	.687	.879	(.806—.928)	0.016	0.045	0.009	14.9
TTPFPROP	s	0.145	0.106	.829	.618	(.387—.772)	0.030	0.084	0.021	73.4
TTPPPROP	s	0.246	0.047	.595	.881	(.809—.929)	0.016	0.045	0.009	19.1
MFPROP	N	1176	147	.965	.963	(.941—.978)	28	78	29	12.5
rMFPROP	N·kg^−1	17.9	1.3	.551	.867	(.786—.921)	0.5	1.3	0.3	7.2
MPPROP	W	1598	290	.874	.945	(.911—.967)	68	189	58	18.2
rMPPROP	W·kg^−1	24.2	3.0	.462	.860	(.774—.916)	1.1	3.1	0.6	12.4
VPROP	m·s^−1	1.45	0.14	.680	.870	(.791—.923)	0.05	0.14	0.03	9.6
DPROP	m	0.45	0.08	.920	.934	(.895—.961)	0.02	0.06	0.02	17.7
NIPROP	N·s	162	24	.969	.983	(.973—.990)	3	9	5	1.0
rNIPROP	N·s·kg^−1	2.46	0.18	.894	.925	(.880—.955)	0.05	0.14	0.04	7.5

ICC = intraclass correlation coefficient; 95% CI = 95% confidence interval; SEM = standard error of measurement; MD = minimum difference to be considered real; SWC = smallest worthwhile change; %CV = percentage coefficient of variation; T_PROP = propulsive sub-phase duration; TTPF_PROP = time from the initiation of the propulsive sub-phase to peak force; TTPF_PROP = time from the initiation of the propulsive sub-phase to peak power; MF_PROP = propulsive sub-phase mean force; rMF_PROP = propulsive sub-phase relative mean force; MP_PROP = propulsive sub-phase mean power; rMP_PROP = propulsive sub-phase relative mean power; V_PROP = propulsive sub-phase mean velocity; D_PROP = propulsive sub-phase displacement; NI_PROP = propulsive sub-phase net impulse; rNI_PROP = propulsive sub-phase relative net impulse.

Table 6. Sub-phases based on the force curve

Variables	Units	Mean	SD	p	ICC	95% CI	SEM	MD	SWC	CV%
TFINC	s	0.736	0.120	.185	.760	(.616—.856)	0.059	0.163	0.024	16.3
MFINC	N	922	119	.819	.970	(.952—.982)	21	57	24	12.9
rMFINC	N·kg^−1	14.0	0.9	.537	.845	(.752—.907)	0.3	0.9	0.2	6.2

ICC = intraclass correlation coefficient; 95% CI = 95% confidence interval; SEM = standard error of measurement; MD = minimum difference to be considered real; SWC = smallest worthwhile change; %CV = percentage coefficient of variation; TF_INC = increasing-force sub-phase duration; MF_INC = mean force of the increasing-force sub-phase; rMF_INC = relative mean force of the increasing-force sub-phase.

Table 7. Sub-phases based on the displacement curve

Variables	Units	Mean	SD	p	ICC	95% CI	SEM	MD	SWC	CV%
TDDEC	s	0.666	0.117	.419	.784	(.665—.871)	0.054	0.151	0.023	17.6
MPDDEC	W	−358	102	.119	.935	(.894—.961)	26	72	20	28.4
rMPDDEC	W·kg^−1	−5.4	1.3	.087	.913	(.860—.948)	0.4	1.1	0.3	24.5
VDDEC	m·s^−1	−0.55	0.14	.087	.913	(.860—.948)	0.04	0.11	0.03	24.6

ICC = intraclass correlation coefficient; 95% CI = 95% confidence interval; SEM = standard error of measurement; MD = minimum difference to be considered real; SWC = smallest worthwhile change; %CV = percentage coefficient of variation; TD_DEC = decreasing-displacement sub-phase duration; MPD_DEC = mean power of the decreasing-displacement sub-phase; rMPD_DEC = relative mean power of the decreasing-displacement sub-phase; VD_DEC = mean velocity of the decreasing-displacement sub-phase.

Table 8. Sub-phases based on velocity-time curve

Variables	Units	Mean	SD	p	ICC	95% CI	SEM	MD	SWC	CV%
Unweighting sub-phase
TUNWEIGHT	s	0.424	0.085	.058	.778	(.638—.868)	0.040	0.111	0.017	20.0
MFUNWEIGHT	N	470	89	.243	.953	(.921—.973)	19	53	18	18.9
rMFUNWEIGHT	N·kg^−1	7.1	1.1	.025*	.922	(.866—.956)	.03	0.8	0.2	15.2
MPUNWEIGHT	W	−202	47	.829	.849	(.757—.910)	18	51	9	23.2
rMPUNWEIGHT	W·kg^−1	−3.1	0.5	.872	.686	(.494—.813)	0.3	0.8	0.1	17.8
VUNWEIGHT	m·s^−1	−0.47	0.12	.086	.901	(.841—.941)	0.04	0.10	0.02	25.4
DUNWEIGHT	m	0.20	0.04	.590	.846	(.753—.908)	0.02	0.05	0.01	22.5
Braking sub-phase
TBRAKE	s	0.242	0.069	.090	.587	(.338—.753)	0.044	0.123	0.014	28.4
TBRAKE-PF	s	0.383	0.151	.345	.604	(.364—.764)	0.095	0.263	0.030	39.4
MFBRAKE	N	960	171	.145	.950	(.919—.970)	38	106	34	17.8
rMFBRAKE	N·kg^−1	14.6	1.9	.051	.895	(.831—.937)	0.6	1.7	0.4	12.8
MPBRAKE	W	−641	231	.278	.937	(.899—.963)	58	161	46	36.1
rMPBRAKE	W·kg^−1	−9.7	3.1	.222	.923	(.876—.954)	0.9	2.4	0.6	32.3
VBRAKE	m·s^−1	−0.71	0.17	.103	.905	(.848—.944)	0.05	0.15	0.03	23.9
DBRAKE	m	0.16	0.04	.476	.806	(.690—.884)	0.02	0.05	0.01	26.1
NIBRAKE	N·s	70	20	.032*	.940	(.898—.965)	5	14	4	29.0
rNIBRAKE	N·s·kg^−1	1.06	0.27	.014*	.921	(.867—.954)	0.07	0.21	0.05	25.2
RFDBRAKE	N·s^−1	2983	1633	.495	.816	(.705—.890)	701	1942	327	548
RFDBRAKE-PF	N·s^−1	2642	1526	.293	.829	(.726—.897)	631	1749	305	57.8

ICC = intraclass correlation coefficient; 95% CI = 95% confidence interval; SEM = standard error of measurement; MD = minimum difference to be considered real; SWC = smallest worthwhile change; %CV = percentage coefficient of variation; T_UNWEIGHT = unweighting sub-phase duration; MF_UNWEIGHT = unweighting sub-phase mean force; rMF_UNWEIGHT = unweighting sub-phase relative mean force; MP_UNWEIGHT = unweighting sub-phase mean power; rMF_UNWEIGHT = unweighting sub-phase relative mean power; V_UNWEIGHT = unweighting sub-phase mean velocity; D_UNWEIGHT = unweighting sub-phase displacement. T_BRAKE = braking sub-phase duration; T_BRAKE-PF = time from the initiation of the braking sub-phase to peak force; MF_BRAKE = braking sub-phase mean force; rMF_BRAKE = braking sub-phase relative mean force; MP_BRAKE = braking sub-phase mean power; rMP_BRAKE = braking sub-phase relative mean power; V_BRAKE = braking sub-phase mean velocity; V_BRAKE = braking sub-phase displacement; NI_BRAKE = braking sub-phase net impulse; rNI_BRAKE = braking sub-phase relative net impulse; RFD_BRAKE = ratio of force development of the braking sub-phase; RFD_BRAKE-PF = rate of force development from the braking sub-phase initiation to PF. * denotes significant differences from session 1 only (p > 0.05).

Table 9. Sub-phases based on force- and displacement-time curves

Variables	Units	Mean	SD	p	ICC	95% CI	SEM	MD	SWC	CV%
Unloading sub-phase
T UNLOAD	S	0.241	0.070	.537	.731	(.570—.839)	0.036	0.100	0.014	29.0
MFUNLOAD	N	489	83	.454	.949	(.918—.969)	19	52	17	17.1
rMFUNLOAD	N·kg^−1	7.4	1.0	.067	.904	(.844—.943)	0.3	0.8	0.2	12.9
MPUNLOAD	W	−63	23	.920	.769	(.628—.862)	11	31	5	37.4
rMPUNLOAD	W·kg^−1	−0.9	0.3	.846	.648	(.433—.790)	0.2	0.5	0.1	32.1
VUNLOAD	m·s^−1	−0.17	0.05	.486	.719	(.548—.832)	0.03	0.07	0.01	29.9
DUNLOAD	m	0.04	0.02	.956	.646	(.429—.789)	0.01	0.03	0.00	44.8
RFDUNLOAD	N·s^−1	−1498	881	.059	.890	(.820—.935)	292	810	176	58.8
Loading sub-phase
TLOAD	s	0.425	0.096	.077	.720	(.553—.832)	0.051	0.140	0.019	22.5
MFLOAD	N	738	98	.783	.949	(.918—.969)	22	61	20	13.2
rMFLOAD	N·kg^−1	11.2	0.7	.342	.643	(.425—.787)	0.4	1.1	0.1	6.1
MPLOAD	W	532	161	.127	.935	(.895—.961)	41	113	32	30.2
rMPLOAD	W·kg^−1	8.0	2.1	.075	.914	(.861—.949)	0.6	1.7	0.4	25.7
VLOAD	m·s^−1	0.78	0.19	.063	.912	(.858—.947)	0.06	0.16	0.04	24.4
DLOAD	m	0.32	0.07	.773	.862	(.778—.918)	0.03	0.07	0.01	22.8
RDFLOAD	N·s^−1	2495	1129	.593	.881	(.809—.929)	389	1079	226	45.2

ICC = intraclass correlation coefficient; 95% CI = 95% confidence interval; SEM = standard error of measurement; MD = minimum difference to be considered real; SWC = smallest worthwhile change; %CV = percentage coefficient of variation; T_UNLOAD = unloading sub-phase duration; MF_UNLOAD = unloading sub-phase mean force; rMF_UNLOAD = unloading sub-phase relative mean force; MP_UNLOAD = unloading sub-phase mean power; rMP_UNLOAD = unloading sub-phase relative mean power; V_UNLOAD = unloading sub-phase mean velocity; D_UNLOAD = unloading sub-phase displacement; RFD_UNLOAD = rate of force development of the unloading sub-phase; T_LOAD = loading sub-phase duration; MF_LOAD = loading sub-phase mean force; rMF_LOAD = loading sub-phase relative mean force; MP_LOAD = loading sub-phase mean power; rMP_LOAD = loading sub-phase relative mean power; V_LOAD = loading sub-phase mean velocity; D_LOAD = loading sub-phase displacement; RFD_LOAD = rate of force development of the loading sub-phase.

Table 10. Transition sub-phase

Variables	Units	Mean	SD	p	ICC	95% CI	SEM	MD	SWC	CV%
TTRANSITION	s	0.183	0.052	.111	.706	(.528—.824)	0.028	0.078	0.010	28.5
MFTRANSITION	N	441	100	.119	.931	(.885—.960)	26	73	20	22.7
rMFTRANSITION	N·kg^−1	6.7	1.3	.020*	.903	(.837—.944)	0.4	1.2	0.3	20.0
MPTRANSITION	W	−388	94	.461	.899	(.838—.939)	30	83	19	24.2
rMPTRANSITION	W·kg^−1	−5.9	1.0	.258	.782	(.651—.869)	0.5	1.3	0.2	17.4
VTRANSITION	m·s^−1	−0.87	0.22	.035*	.915	(.860—.950)	0.06	0.18	0.04	25.1
DTRANSITION	m	0.15	0.04	.566	.759	(.612—.856)	0.02	0.05	0.01	26.2
RFDTRANSITION	N·s^−1	2069	1186	.109	.893	(.827—.937)	388	1075	237	57.3

ICC = intraclass correlation coefficient; 95% CI = 95% confidence interval; SEM = standard error of measurement; MD = minimum difference to be considered real; SWC = smallest worthwhile change; %CV = percentage coefficient of variation; T_TRANSITION = transition sub-phase duration; MF_TRANSITION = transition sub-phase mean force; rMF_TRANSITION = transition sub-phase relative mean force; MP_TRANSITION = transition sub-phase mean power; rMP_TRANSITION = transition sub-phase relative mean power; V_TRANSITION = transition sub-phase mean velocity; D_TRANSITION = transition sub-phase displacement; RFD_TRANSITION = rate of force development of the transition sub-phase. * denotes significant differences from session 1 only (p > 0.05).