Unilateral vs. bilateral hamstring strength assessments: comparing reliability and inter-limb asymmetries in female soccer players

Figures & data

Figure 1. Illustration of the performance of a) ISO 300 (isometric knee flexion at 90) and c) kneeling ISO (isometric knee flexion at 90 prone)

Table 1. Within- and between-session reliability of hamstring strength assessments

	Session 1			Session 2			Between-Session
ISO 30°	Mean (± SD)	% CV	ICC (95% CI)	Mean (± SD)	% CV	ICC (95% CI)	Mean (± SD)	% CV	ICC (95% CI)
Left (N)	154.03 ± 27.05	6.77	0.834 (0.658–0.925)	162.91 ± 24.44	5.20	0.855 (0.737–0.930)	158.15 ± 23.32	8.72	0.762 (0.290–0.815)
Right (N)	153.97 ± 25.42	5.66	0.865 (0.752–0.935)	162.02 ± 24.69	4.85	0.881 (0.780–0.943)	158.00 ± 23.65	6.50	0.857 (0.638–0.941)
ISO 90°
Left (N)	188.88 ± 27.84	5.32	0.824 (0.687–0.914)	189.57 ± 34.46	7.33	0.834 (0.700–0.920)	189.22 ± 27.84	10.23	0.698 (0.274–0.873)
Right (N)	189.70 ± 31.28	5.72	0.842 (0.713–0.923)	195.31 ± 32.22	6.25	0.852 (0.732–0.929)	192.50 ± 28.97	7.52	0.798 (0.530–0.914)
Kneeling ISO
Left (N)	274.86 ± 45.53	6.67	0.812 (0.666–0.908)	278.79 ± 52.44	6.50	0.864 (0.743–0.936)	276.83 ± 46.98	6.27	0.909 (0.788–0.962)
Right (N)	272.86 ± 44.36	7.30	0.786 (0.627–0.962)	269.52 ± 42.36	6.96	0.784 (0.623–0.893)	270.82 ± 37.62	9.10	0.679 (0.231–0.865)
NHE
Left (N)	319.10 ± 46.92	4.72	0.871 (0.742–0.937)	322.28 ± 50.19	4.88	0.819 (0.696–0.903)	320.60 ± 46.83	2.89	0.963 (0.790–0.983)
Right (N)	332.07 ± 43.51	4.24	0.869 (0.759–0.934)	326.65 ± 45.64	4.86	0.823 (0.702–0.906)	329.36 ± 42.54	4.01	0.901 (0.790–0.953)

ISO = Isometric; SD = Standard deviation; CV = coefficient of variation; ICC = Intraclass correlation coefficient; CI = Confidence interval; N = Newtons; NHE = Nordic hamstring exercise

Figure 2. Comparison of peak force of the left and right limb during a) ISO (isometric knee flexion at 30), b) IS) 90 (isometric knee flexion at 90) and c) Kneeling ISO (isometric knee flexion at 90 prone and d) NHE (Nordic hamstring excercise) between testing sessions. Individual data is plotted opn the upper axes. Paired mean difference are plotted as a boopstrap sampling distribution. mean dissference arc depicted as dots; 95% confidence intervals are indicated by the ends of the vertical error bars

Table 2. Differences between-session comparisons within- and between-limb

	Session 1 vs Session 2
	Left			Right			Left – Right Asymmetry
	p	g	% diff	p	g	% diff	p	g	% diff	Kappa Coefficient	Agreement Descriptor
ISO 30°	0.086	0.31	5.08	0.029a	0.32	4.97	0.386	0.29	21.05	0.03	Slight
ISO 90°	0.915	0.02	0.36	0.312	0.17	2.87	0.064	0.49	30.77	0.31	Fair
Kneeling ISO	0.261	0.08	1.41	0.656	−0.06	−0.96	0.484	0.24	49.36	0.47	Moderate
NHE	0.079	0.06	0.93	0.237	−0.12	−1.66	0.150	−0.21	16.51	0.62	Substantial

% diff = Percentage difference; ISO = Isometric; NHE = Nordic hamstring exercise

a= significant p< 0.05

Figure 3. Individual asymmetry data for peak force during a0 ISO 30 (isometric knee flexion at 30), b) ISO 90 (isometric knee flexion at 90) and c) Kneeling ISO (isometric knee flexion at 90 prone) and d) NHE (Nordic hamstring excercise). Above the x axis signifies right limb dominance, below signifies left limb dominance

Table 3. The magnitude and direction of asymmetries within-session

	Left – Right Asymmetry (Mean ± SD)
	Session 1	Session 2
ISO 30° (%)	0.09 ± 9.43	−0.24 ± 11.36
ISO 90° (%)	0.11 ± 12.84	2.90 ± 16.07
Kneeling ISO (%)	−0.89 ± 10.62	−2.76 ± 13.94
NHE (%)	3.94 ± 7.41	1.49 ± 7.80

SD = Standard deviation; ISO = Isometric; NHE = Nordic hamstring exercise

Note: Positive values demonstrate right limb dominance, negative values demonstrate left limb dominance

Data availability statement

The data that support the findings of this study are available upon reasonable request from the corresponding author.