The effect of unilateral training on contralateral limb strength in young, older, and patient populations: a meta-analysis of cross education

Figures & data

Figure 1. Flow diagram of the identification and review process.

Figure 2. Forest plot of standardized mean difference (SMD) for each young unit included in the analysis for the untrained (cross education) limb. Light grey lines indicate cutoff values for small (0.2), moderate (0.5), and large (0.8) effect sizes.

Figure 3. Forest plot of standardized mean difference (SMD) for each older (A) and patient (B) unit included in the analysis for the untrained (cross education) limb. Light grey lines indicate cutoff values for small (0.2), moderate (0.5), and large (0.8) effect sizes. DF: dorsiflexion; KE: knee extension; MS: multiple sclerosis; OA: osteoarthritis.

Table 1. Median and range of training characteristics.

Training characteristic	Young	Older	Patients
	Median (range)
Number of training sessions	21 (6–84)	27 (6–36)	18 (16–27)
Training volume (sets x reps)	30 (3–250)	34 (20–40)	33 (24–42)
Training intensity (% maximum)	100 (10–100)	100 (70–100)	100 (80–100)

Table 2. Effect size (standardized mean difference), percent gain, and controlled percent gain for the untrained (contralateral) limb.

	N (units)	Effect size (95% CI)	N (units)	% gain	Cross-body transfer
Young	86	0.71 (0.60, 0.83)**	126	18	70%
Isometric	24	0.73 (0.56, 0.89)**	37	15	65%
Isokinetic	23	0.61 (0.41, 0.80)**	31	20	70%
Dynamic	27	0.65 (0.43, 0.86)**	41	18	71%
EMS	6	1.57 (0.81, 2.33)**	10	27	77%
Other	6	0.46 (0.18, 0.74)**	7	12	80%
Older	6	0.58 (0.22, 0.94)**	9	15	48%
Patients	4	0.76 (0.21, 1.31)**	6	29	77%
Control limb	38	0.10 (–0.04, 0.23)	48	2.2	–

CI: confidence interval; EMS: electromyostimulation. , **p < 0.001, for effect size only. Cross-body transfer is the amount of strength gain transferred from the ipsilateral limb to the contralateral limb.

Table 3. Effect size (standardized mean difference), percent gain, and controlled percent gain for the trained (ipsilateral) limb.

	N (units)	Effect size (95% CI)	N (units)	% gain
Young	81	1.11 (0.96, 1.25)**	123	29
Isometric	25	1.11 (0.90, 1.32)**	37	25
Isokinetic	20	0.95 (0.79, 1.11)**	30	31
Dynamic	23	1.18 (0.89, 1.47)**	39	31
EMS	7	1.87 (0.93, 2.82)**	10	35
Other	6	0.53 (0.24, 0.81)**	7	15
Elderly	6	1.44 (1.00, 1.87)**	9	31
Patients	2	0.56 (0.11, 1.01)*	4	29
Control limb	32	0.13 (–0.02. 0.27)	39	3.0

CI: confidence interval; EMS: electromyostimulation. *p < 0.05, ** p < 0.001, for effect size only.

Table 4. The number of units that fall within each category: sex of the unit, the usage of familiarization, the limb involved, and the presence of a control group from the able-bodied participants.

	Number of units	Number of participants	% gain (untrained)	% gain (trained)	Cross-body transfer
Overall: able-bodied	135	2362	29	18	68%
Limb trained
Lower	68	791	18	28	68%
Upper	67	1571	17	30	69%
Sex of unit
Males only	65	997	16	26	65%
Females only	27	747	17	33	54%
Both sexes	34	506
Unknown sex	9	112
Familiarized
Yes	67	1387	18	29
No	68	975	17	29
Control group (Y/N)	79/56

Note: the presence of a control group (‘Y’) does not indicate the reporting of control results. *significant difference in % gain or cross-body transfer between unit categories (lower vs upper; males vs females; yes vs no familiarization), p < 0.05.